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 $65.82   13.136%   $74.4661   $74.47   $74.45   $74.50  
  Purchase #2 $109.46   5.242%   $115.1979   $115.20   $115.20   $115.20  
  Purchase #3 $121.80   3.374%   $125.9095   $125.91   $125.90   $125.90  
  Purchase #4 $60.71   9.524%   $66.492   $66.49   $66.50   $66.50  
  Purchase #5 $174.91   8.680%   $190.0922   $190.09   $190.10   $190.10  
  Purchase #6 $32.35   11.296%   $36.0043   $36.00   $36.00   $36.00  
  Purchase #7 $216.38   4.350%   $225.7925   $225.79   $225.80   $225.80  
  7 purchase totals = $781.43       $833.9545   $833.95   $833.95   $834.00