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 $167.66   13.624%   $190.502   $190.50   $190.50   $190.50  
  Purchase #2 $108.67   4.684%   $113.7601   $113.76   $113.75   $113.80  
  Purchase #3 $14.35   7.151%   $15.3762   $15.38   $15.40   $15.40  
  Purchase #4 $69.67   4.780%   $73.0002   $73.00   $73.00   $73.00  
  Purchase #5 $87.71   7.739%   $94.4979   $94.50   $94.50   $94.50  
  Purchase #6 $146.98   13.375%   $166.6386   $166.64   $166.65   $166.60  
  Purchase #7 $120.90   9.762%   $132.7023   $132.70   $132.70   $132.70  
  7 purchase totals = $715.94       $786.4773   $786.48   $786.50   $786.50