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 $214.39   12.852%   $241.9434   $241.94   $241.95   $241.90  
  Purchase #2 $235.78   5.741%   $249.3161   $249.32   $249.30   $249.30  
  Purchase #3 $169.73   13.619%   $192.8455   $192.85   $192.85   $192.80  
  Purchase #4 $200.98   13.267%   $227.644   $227.64   $227.65   $227.60  
  Purchase #5 $139.68   10.191%   $153.9148   $153.91   $153.90   $153.90  
  Purchase #6 $248.95   8.496%   $270.1008   $270.10   $270.10   $270.10  
  Purchase #7 $68.29   6.424%   $72.6769   $72.68   $72.70   $72.70  
  7 purchase totals = $1,277.80       $1,408.4415   $1,408.44   $1,408.45   $1,408.30