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 $60.83   6.250%   $64.6319   $64.63   $64.65   $64.60  
  Purchase #2 $109.72   12.765%   $123.7258   $123.73   $123.75   $123.70  
  Purchase #3 $132.90   12.483%   $149.4899   $149.49   $149.50   $149.50  
  Purchase #4 $245.65   6.522%   $261.6713   $261.67   $261.65   $261.70  
  Purchase #5 $15.36   7.307%   $16.4824   $16.48   $16.50   $16.50  
  Purchase #6 $240.28   7.559%   $258.4428   $258.44   $258.45   $258.40  
  Purchase #7 $57.39   5.621%   $60.6159   $60.62   $60.60   $60.60  
  7 purchase totals = $862.13       $935.0600   $935.06   $935.10   $935.00