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 $232.67   10.159%   $256.3069   $256.31   $256.30   $256.30  
  Purchase #2 $210.42   4.368%   $219.6111   $219.61   $219.60   $219.60  
  Purchase #3 $132.80   5.385%   $139.9513   $139.95   $139.95   $140.00  
  Purchase #4 $188.84   6.105%   $200.3687   $200.37   $200.35   $200.40  
  Purchase #5 $153.70   5.337%   $161.903   $161.90   $161.90   $161.90  
  Purchase #6 $236.84   3.803%   $245.847   $245.85   $245.85   $245.80  
  Purchase #7 $164.68   3.475%   $170.4026   $170.40   $170.40   $170.40  
  7 purchase totals = $1,319.95       $1,394.3906   $1,394.39   $1,394.35   $1,394.40