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 $226.72   6.719%   $241.9533   $241.95   $241.95   $242.00  
  Purchase #2 $18.97   10.429%   $20.9484   $20.95   $20.95   $20.90  
  Purchase #3 $111.67   13.113%   $126.3133   $126.31   $126.30   $126.30  
  Purchase #4 $182.61   11.132%   $202.9381   $202.94   $202.95   $202.90  
  Purchase #5 $227.84   4.537%   $238.1771   $238.18   $238.20   $238.20  
  Purchase #6 $152.50   5.221%   $160.462   $160.46   $160.45   $160.50  
  Purchase #7 $30.51   5.389%   $32.1542   $32.15   $32.15   $32.20  
  7 purchase totals = $950.82       $1,022.9464   $1,022.94   $1,022.95   $1,023.00