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 $245.26   6.265%   $260.6255   $260.63   $260.65   $260.60  
  Purchase #2 $134.87   4.148%   $140.4644   $140.46   $140.45   $140.50  
  Purchase #3 $83.68   4.571%   $87.505   $87.51   $87.50   $87.50  
  Purchase #4 $120.39   8.439%   $130.5497   $130.55   $130.55   $130.50  
  Purchase #5 $225.73   12.630%   $254.2397   $254.24   $254.25   $254.20  
  Purchase #6 $84.55   13.484%   $95.9507   $95.95   $95.95   $96.00  
  Purchase #7 $71.53   5.568%   $75.5128   $75.51   $75.50   $75.50  
  7 purchase totals = $966.01       $1,044.8478   $1,044.85   $1,044.85   $1,044.80