Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $34.91   4.679%   $36.5434   $36.54   $36.55   $36.50  
  Purchase #2 $163.35   3.355%   $168.8304   $168.83   $168.85   $168.80  
  Purchase #3 $187.92   6.390%   $199.9281   $199.93   $199.95   $199.90  
  Purchase #4 $123.75   7.198%   $132.6575   $132.66   $132.65   $132.70  
  Purchase #5 $176.69   5.368%   $186.1747   $186.17   $186.15   $186.20  
  Purchase #6 $210.72   3.676%   $218.4661   $218.47   $218.45   $218.50  
  Purchase #7 $86.72   5.337%   $91.3482   $91.35   $91.35   $91.30  
  7 purchase totals = $984.06       $1,033.9484   $1,033.95   $1,033.95   $1,033.90