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 $141.68   9.220%   $154.7429   $154.74   $154.75   $154.70  
  Purchase #2 $53.73   13.757%   $61.1216   $61.12   $61.10   $61.10  
  Purchase #3 $58.34   13.464%   $66.1949   $66.19   $66.20   $66.20  
  Purchase #4 $168.89   3.811%   $175.3264   $175.33   $175.35   $175.30  
  Purchase #5 $144.92   11.624%   $161.7655   $161.77   $161.75   $161.80  
  Purchase #6 $163.92   11.517%   $182.7987   $182.80   $182.80   $182.80  
  Purchase #7 $157.61   9.203%   $172.1148   $172.11   $172.10   $172.10  
  7 purchase totals = $889.09       $974.0648   $974.06   $974.05   $974.00