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 $61.85   9.833%   $67.9317   $67.93   $67.95   $67.90  
  Purchase #2 $152.41   3.195%   $157.2795   $157.28   $157.30   $157.30  
  Purchase #3 $93.96   7.824%   $101.3114   $101.31   $101.30   $101.30  
  Purchase #4 $5.95   5.150%   $6.2564   $6.26   $6.25   $6.30  
  Purchase #5 $195.66   10.368%   $215.946   $215.95   $215.95   $215.90  
  Purchase #6 $240.54   11.206%   $267.4949   $267.49   $267.50   $267.50  
  Purchase #7 $87.64   10.383%   $96.7397   $96.74   $96.75   $96.70  
  7 purchase totals = $838.01       $912.9596   $912.96   $913.00   $912.90