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 $248.93   13.150%   $281.6643   $281.66   $281.65   $281.70  
  Purchase #2 $115.85   8.762%   $126.0008   $126.00   $126.00   $126.00  
  Purchase #3 $14.30   9.592%   $15.6717   $15.67   $15.65   $15.70  
  Purchase #4 $173.72   12.316%   $195.1154   $195.12   $195.10   $195.10  
  Purchase #5 $134.53   10.191%   $148.24   $148.24   $148.25   $148.20  
  Purchase #6 $104.46   10.117%   $115.0282   $115.03   $115.05   $115.00  
  Purchase #7 $66.60   11.344%   $74.1551   $74.16   $74.15   $74.20  
  7 purchase totals = $858.39       $955.8755   $955.88   $955.85   $955.90