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 $54.91   4.571%   $57.4199   $57.42   $57.40   $57.40  
  Purchase #2 $40.64   9.860%   $44.6471   $44.65   $44.65   $44.60  
  Purchase #3 $43.64   12.315%   $49.0143   $49.01   $49.00   $49.00  
  Purchase #4 $46.69   8.703%   $50.7534   $50.75   $50.75   $50.80  
  Purchase #5 $249.35   6.346%   $265.1738   $265.17   $265.15   $265.20  
  Purchase #6 $250.56   11.216%   $278.6628   $278.66   $278.65   $278.70  
  Purchase #7 $166.29   9.575%   $182.2123   $182.21   $182.20   $182.20  
  7 purchase totals = $852.08       $927.8836   $927.87   $927.80   $927.90