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 $48.75   5.445%   $51.4044   $51.40   $51.40   $51.40  
  Purchase #2 $212.47   9.348%   $232.3317   $232.33   $232.35   $232.30  
  Purchase #3 $78.30   11.583%   $87.3695   $87.37   $87.35   $87.40  
  Purchase #4 $151.57   6.666%   $161.6737   $161.67   $161.65   $161.70  
  Purchase #5 $86.63   12.479%   $97.4406   $97.44   $97.45   $97.40  
  Purchase #6 $226.77   3.234%   $234.1037   $234.10   $234.10   $234.10  
  Purchase #7 $116.55   5.547%   $123.015   $123.02   $123.00   $123.00  
  7 purchase totals = $921.04       $987.3386   $987.33   $987.30   $987.30