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 $239.73   9.118%   $261.5886   $261.59   $261.60   $261.60  
  Purchase #2 $245.68   7.291%   $263.5925   $263.59   $263.60   $263.60  
  Purchase #3 $47.45   9.302%   $51.8638   $51.86   $51.85   $51.90  
  Purchase #4 $61.91   3.573%   $64.122   $64.12   $64.10   $64.10  
  Purchase #5 $187.65   7.414%   $201.5624   $201.56   $201.55   $201.60  
  Purchase #6 $18.51   12.544%   $20.8319   $20.83   $20.85   $20.80  
  Purchase #7 $185.70   13.135%   $210.0917   $210.09   $210.10   $210.10  
  7 purchase totals = $986.63       $1,073.6529   $1,073.64   $1,073.65   $1,073.70