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 $199.52   13.379%   $226.2138   $226.21   $226.20   $226.20  
  Purchase #2 $140.78   4.511%   $147.1306   $147.13   $147.15   $147.10  
  Purchase #3 $164.73   12.677%   $185.6128   $185.61   $185.60   $185.60  
  Purchase #4 $51.69   4.676%   $54.107   $54.11   $54.10   $54.10  
  Purchase #5 $216.34   11.573%   $241.377   $241.38   $241.40   $241.40  
  Purchase #6 $46.47   4.571%   $48.5941   $48.59   $48.60   $48.60  
  Purchase #7 $53.58   4.514%   $55.9986   $56.00   $56.00   $56.00  
  7 purchase totals = $873.11       $959.0339   $959.03   $959.05   $959.00