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 $53.59   13.256%   $60.6939   $60.69   $60.70   $60.70  
  Purchase #2 $116.73   10.617%   $129.1232   $129.12   $129.10   $129.10  
  Purchase #3 $105.33   10.204%   $116.0779   $116.08   $116.10   $116.10  
  Purchase #4 $231.49   12.816%   $261.1578   $261.16   $261.15   $261.20  
  Purchase #5 $50.43   11.135%   $56.0454   $56.05   $56.05   $56.00  
  Purchase #6 $112.61   6.379%   $119.7934   $119.79   $119.80   $119.80  
  Purchase #7 $64.89   11.430%   $72.3069   $72.31   $72.30   $72.30  
  7 purchase totals = $735.07       $815.1985   $815.20   $815.20   $815.20