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 $44.86   6.614%   $47.827   $47.83   $47.85   $47.80  
  Purchase #2 $111.95   4.425%   $116.9038   $116.90   $116.90   $116.90  
  Purchase #3 $111.63   9.747%   $122.5106   $122.51   $122.50   $122.50  
  Purchase #4 $26.34   13.428%   $29.8769   $29.88   $29.90   $29.90  
  Purchase #5 $134.46   4.238%   $140.1584   $140.16   $140.15   $140.20  
  Purchase #6 $49.40   3.669%   $51.2125   $51.21   $51.20   $51.20  
  Purchase #7 $235.97   3.390%   $243.9694   $243.97   $243.95   $244.00  
  7 purchase totals = $714.61       $752.4586   $752.46   $752.45   $752.50