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 $222.68   8.536%   $241.688   $241.69   $241.70   $241.70  
  Purchase #2 $67.84   4.141%   $70.6493   $70.65   $70.65   $70.60  
  Purchase #3 $88.70   8.851%   $96.5508   $96.55   $96.55   $96.60  
  Purchase #4 $166.46   10.174%   $183.3956   $183.40   $183.40   $183.40  
  Purchase #5 $32.36   9.754%   $35.5164   $35.52   $35.50   $35.50  
  Purchase #6 $105.96   7.693%   $114.1115   $114.11   $114.10   $114.10  
  Purchase #7 $139.37   9.508%   $152.6213   $152.62   $152.60   $152.60  
  7 purchase totals = $823.37       $894.5329   $894.54   $894.50   $894.50