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 $91.88   4.654%   $96.1561   $96.16   $96.15   $96.20  
  Purchase #2 $221.35   3.592%   $229.3009   $229.30   $229.30   $229.30  
  Purchase #3 $42.33   9.351%   $46.2883   $46.29   $46.30   $46.30  
  Purchase #4 $215.58   11.598%   $240.583   $240.58   $240.60   $240.60  
  Purchase #5 $230.32   10.188%   $253.785   $253.79   $253.80   $253.80  
  Purchase #6 $236.79   5.661%   $250.1947   $250.19   $250.20   $250.20  
  Purchase #7 $189.33   10.852%   $209.8761   $209.88   $209.90   $209.90  
  7 purchase totals = $1,227.58       $1,326.1841   $1,326.19   $1,326.25   $1,326.30