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 $151.58   11.670%   $169.2694   $169.27   $169.25   $169.30  
  Purchase #2 $249.89   13.123%   $282.6831   $282.68   $282.70   $282.70  
  Purchase #3 $83.59   13.613%   $94.9691   $94.97   $94.95   $95.00  
  Purchase #4 $115.64   8.553%   $125.5307   $125.53   $125.55   $125.50  
  Purchase #5 $17.29   9.462%   $18.926   $18.93   $18.95   $18.90  
  Purchase #6 $71.60   6.406%   $76.1867   $76.19   $76.20   $76.20  
  Purchase #7 $66.33   11.194%   $73.755   $73.76   $73.75   $73.80  
  7 purchase totals = $755.92       $841.3200   $841.33   $841.35   $841.40