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 $68.25   11.802%   $76.3049   $76.30   $76.30   $76.30  
  Purchase #2 $31.35   10.384%   $34.6054   $34.61   $34.60   $34.60  
  Purchase #3 $78.28   7.582%   $84.2152   $84.22   $84.20   $84.20  
  Purchase #4 $171.76   9.779%   $188.5564   $188.56   $188.55   $188.60  
  Purchase #5 $209.67   8.279%   $227.0286   $227.03   $227.05   $227.00  
  Purchase #6 $14.74   3.401%   $15.2413   $15.24   $15.25   $15.20  
  Purchase #7 $86.30   11.362%   $96.1054   $96.11   $96.10   $96.10  
  7 purchase totals = $660.35       $722.0572   $722.07   $722.05   $722.00