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 $64.78   10.281%   $71.44   $71.44   $71.45   $71.40  
  Purchase #2 $84.67   4.345%   $88.3489   $88.35   $88.35   $88.30  
  Purchase #3 $90.77   7.285%   $97.3826   $97.38   $97.40   $97.40  
  Purchase #4 $98.83   5.761%   $104.5236   $104.52   $104.50   $104.50  
  Purchase #5 $173.58   12.529%   $195.3278   $195.33   $195.35   $195.30  
  Purchase #6 $66.66   5.537%   $70.351   $70.35   $70.35   $70.40  
  Purchase #7 $178.54   11.220%   $198.5722   $198.57   $198.55   $198.60  
  7 purchase totals = $757.83       $825.9461   $825.94   $825.95   $825.90