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 $84.48   11.678%   $94.3456   $94.35   $94.35   $94.30  
  Purchase #2 $215.93   7.176%   $231.4251   $231.43   $231.45   $231.40  
  Purchase #3 $43.52   9.139%   $47.4973   $47.50   $47.50   $47.50  
  Purchase #4 $55.55   12.356%   $62.4138   $62.41   $62.40   $62.40  
  Purchase #5 $111.71   13.646%   $126.9539   $126.95   $126.95   $127.00  
  Purchase #6 $246.61   7.128%   $264.1884   $264.19   $264.20   $264.20  
  Purchase #7 $33.62   9.265%   $36.7349   $36.73   $36.75   $36.70  
  7 purchase totals = $791.42       $863.5590   $863.56   $863.60   $863.50