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 $248.86   6.550%   $265.1603   $265.16   $265.15   $265.20  
  Purchase #2 $69.39   9.315%   $75.8537   $75.85   $75.85   $75.90  
  Purchase #3 $53.61   8.566%   $58.2022   $58.20   $58.20   $58.20  
  Purchase #4 $49.54   9.768%   $54.3791   $54.38   $54.40   $54.40  
  Purchase #5 $43.75   11.466%   $48.7664   $48.77   $48.75   $48.80  
  Purchase #6 $130.31   3.242%   $134.5347   $134.53   $134.55   $134.50  
  Purchase #7 $236.41   12.843%   $266.7721   $266.77   $266.75   $266.80  
  7 purchase totals = $831.87       $903.6685   $903.66   $903.65   $903.80