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 $250.27   9.551%   $274.1733   $274.17   $274.15   $274.20  
  Purchase #2 $134.66   11.580%   $150.2536   $150.25   $150.25   $150.30  
  Purchase #3 $83.66   10.808%   $92.702   $92.70   $92.70   $92.70  
  Purchase #4 $186.89   4.824%   $195.9056   $195.91   $195.90   $195.90  
  Purchase #5 $17.76   3.780%   $18.4313   $18.43   $18.45   $18.40  
  Purchase #6 $99.41   3.554%   $102.943   $102.94   $102.95   $102.90  
  Purchase #7 $175.82   7.804%   $189.541   $189.54   $189.55   $189.50  
  7 purchase totals = $948.47       $1,023.9498   $1,023.94   $1,023.95   $1,023.90