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 $55.47   12.144%   $62.2063   $62.21   $62.20   $62.20  
  Purchase #2 $146.54   4.844%   $153.6384   $153.64   $153.65   $153.60  
  Purchase #3 $132.43   9.113%   $144.4983   $144.50   $144.50   $144.50  
  Purchase #4 $245.79   6.578%   $261.9581   $261.96   $261.95   $262.00  
  Purchase #5 $225.66   6.492%   $240.3098   $240.31   $240.30   $240.30  
  Purchase #6 $172.97   6.612%   $184.4068   $184.41   $184.40   $184.40  
  Purchase #7 $156.67   8.589%   $170.1264   $170.13   $170.15   $170.10  
  7 purchase totals = $1,135.53       $1,217.1441   $1,217.16   $1,217.15   $1,217.10