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 $10.65   8.129%   $11.5157   $11.52   $11.50   $11.50  
  Purchase #2 $196.38   9.768%   $215.5624   $215.56   $215.55   $215.60  
  Purchase #3 $24.31   11.111%   $27.0111   $27.01   $27.00   $27.00  
  Purchase #4 $55.36   12.745%   $62.4156   $62.42   $62.40   $62.40  
  Purchase #5 $25.29   13.334%   $28.6622   $28.66   $28.65   $28.70  
  Purchase #6 $208.43   5.394%   $219.6727   $219.67   $219.65   $219.70  
  Purchase #7 $155.40   8.582%   $168.7364   $168.74   $168.75   $168.70  
  7 purchase totals = $675.82       $733.5761   $733.58   $733.50   $733.60