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 $46.90   12.789%   $52.898   $52.90   $52.90   $52.90  
  Purchase #2 $63.40   11.258%   $70.5376   $70.54   $70.55   $70.50  
  Purchase #3 $107.59   4.334%   $112.253   $112.25   $112.25   $112.30  
  Purchase #4 $231.50   12.313%   $260.0046   $260.00   $260.00   $260.00  
  Purchase #5 $122.98   10.355%   $135.7146   $135.71   $135.70   $135.70  
  Purchase #6 $35.36   10.352%   $39.0205   $39.02   $39.00   $39.00  
  Purchase #7 $81.48   12.134%   $91.3668   $91.37   $91.35   $91.40  
  7 purchase totals = $689.21       $761.7951   $761.79   $761.75   $761.80