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 $150.67   8.307%   $163.1862   $163.19   $163.20   $163.20  
  Purchase #2 $200.98   3.638%   $208.2917   $208.29   $208.30   $208.30  
  Purchase #3 $121.76   4.176%   $126.8447   $126.84   $126.85   $126.80  
  Purchase #4 $71.51   4.584%   $74.788   $74.79   $74.80   $74.80  
  Purchase #5 $15.29   13.211%   $17.31   $17.31   $17.30   $17.30  
  Purchase #6 $143.27   13.533%   $162.6587   $162.66   $162.65   $162.70  
  Purchase #7 $188.60   11.175%   $209.6761   $209.68   $209.70   $209.70  
  7 purchase totals = $892.08       $962.7554   $962.76   $962.80   $962.80