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 $82.32   13.450%   $93.392   $93.39   $93.40   $93.40  
  Purchase #2 $56.91   5.355%   $59.9575   $59.96   $59.95   $60.00  
  Purchase #3 $180.35   3.843%   $187.2809   $187.28   $187.30   $187.30  
  Purchase #4 $68.85   9.360%   $75.2944   $75.29   $75.30   $75.30  
  Purchase #5 $97.32   4.733%   $101.9262   $101.93   $101.95   $101.90  
  Purchase #6 $117.80   12.477%   $132.4979   $132.50   $132.50   $132.50  
  Purchase #7 $84.82   12.237%   $95.1994   $95.20   $95.20   $95.20  
  7 purchase totals = $688.37       $745.5483   $745.55   $745.60   $745.60