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 $91.44   4.309%   $95.3801   $95.38   $95.40   $95.40  
  Purchase #2 $130.79   7.553%   $140.6686   $140.67   $140.65   $140.70  
  Purchase #3 $19.89   7.199%   $21.3219   $21.32   $21.30   $21.30  
  Purchase #4 $60.99   6.128%   $64.7275   $64.73   $64.75   $64.70  
  Purchase #5 $196.26   4.848%   $205.7747   $205.77   $205.75   $205.80  
  Purchase #6 $44.76   8.363%   $48.5033   $48.50   $48.50   $48.50  
  Purchase #7 $14.34   10.144%   $15.7946   $15.79   $15.80   $15.80  
  7 purchase totals = $558.47       $592.1707   $592.16   $592.15   $592.20