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 $111.88   12.742%   $126.1357   $126.14   $126.15   $126.10  
  Purchase #2 $107.72   5.172%   $113.2913   $113.29   $113.30   $113.30  
  Purchase #3 $48.82   11.121%   $54.2493   $54.25   $54.25   $54.20  
  Purchase #4 $68.27   4.285%   $71.1954   $71.20   $71.20   $71.20  
  Purchase #5 $232.83   5.145%   $244.8091   $244.81   $244.80   $244.80  
  Purchase #6 $149.32   12.513%   $168.0044   $168.00   $168.00   $168.00  
  Purchase #7 $50.42   6.873%   $53.8854   $53.89   $53.90   $53.90  
  7 purchase totals = $769.26       $831.5706   $831.58   $831.60   $831.50