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 $49.74   13.676%   $56.5424   $56.54   $56.55   $56.50  
  Purchase #2 $131.63   4.576%   $137.6534   $137.65   $137.65   $137.70  
  Purchase #3 $124.56   9.533%   $136.4343   $136.43   $136.45   $136.40  
  Purchase #4 $140.27   5.830%   $148.4477   $148.45   $148.45   $148.40  
  Purchase #5 $88.78   9.286%   $97.0241   $97.02   $97.00   $97.00  
  Purchase #6 $26.84   10.465%   $29.6488   $29.65   $29.65   $29.60  
  Purchase #7 $161.36   5.733%   $170.6108   $170.61   $170.60   $170.60  
  7 purchase totals = $723.18       $776.3615   $776.35   $776.35   $776.20