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 $72.65   3.671%   $75.317   $75.32   $75.30   $75.30  
  Purchase #2 $212.43   10.257%   $234.2189   $234.22   $234.20   $234.20  
  Purchase #3 $197.65   5.525%   $208.5702   $208.57   $208.55   $208.60  
  Purchase #4 $217.84   11.733%   $243.3992   $243.40   $243.40   $243.40  
  Purchase #5 $196.32   10.728%   $217.3812   $217.38   $217.40   $217.40  
  Purchase #6 $170.61   13.843%   $194.2275   $194.23   $194.25   $194.20  
  Purchase #7 $67.50   12.130%   $75.6878   $75.69   $75.70   $75.70  
  7 purchase totals = $1,135.00       $1,248.8018   $1,248.81   $1,248.80   $1,248.80