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 $48.54   5.108%   $51.0194   $51.02   $51.00   $51.00  
  Purchase #2 $76.49   6.186%   $81.2217   $81.22   $81.20   $81.20  
  Purchase #3 $211.63   12.205%   $237.4594   $237.46   $237.45   $237.50  
  Purchase #4 $222.94   5.234%   $234.6087   $234.61   $234.60   $234.60  
  Purchase #5 $41.42   13.313%   $46.9342   $46.93   $46.95   $46.90  
  Purchase #6 $52.79   4.251%   $55.0341   $55.03   $55.05   $55.00  
  Purchase #7 $96.64   4.611%   $101.0961   $101.10   $101.10   $101.10  
  7 purchase totals = $750.45       $807.3736   $807.37   $807.35   $807.30