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 $235.56   13.541%   $267.4572   $267.46   $267.45   $267.50  
  Purchase #2 $200.78   10.675%   $222.2133   $222.21   $222.20   $222.20  
  Purchase #3 $231.28   11.438%   $257.7338   $257.73   $257.75   $257.70  
  Purchase #4 $116.46   4.845%   $122.1025   $122.10   $122.10   $122.10  
  Purchase #5 $37.26   9.505%   $40.8016   $40.80   $40.80   $40.80  
  Purchase #6 $92.53   13.686%   $105.1937   $105.19   $105.20   $105.20  
  Purchase #7 $119.56   4.543%   $124.9916   $124.99   $125.00   $125.00  
  7 purchase totals = $1,033.43       $1,140.4937   $1,140.48   $1,140.50   $1,140.50