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 $51.84   4.211%   $54.023   $54.02   $54.00   $54.00  
  Purchase #2 $70.58   12.804%   $79.6171   $79.62   $79.60   $79.60  
  Purchase #3 $57.68   12.547%   $64.9171   $64.92   $64.90   $64.90  
  Purchase #4 $22.84   6.323%   $24.2842   $24.28   $24.30   $24.30  
  Purchase #5 $61.60   4.680%   $64.4829   $64.48   $64.50   $64.50  
  Purchase #6 $20.69   8.758%   $22.502   $22.50   $22.50   $22.50  
  Purchase #7 $46.46   13.782%   $52.8631   $52.86   $52.85   $52.90  
  7 purchase totals = $331.69       $362.6894   $362.68   $362.65   $362.70