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 $81.57   13.118%   $92.2704   $92.27   $92.25   $92.30  
  Purchase #2 $247.75   8.322%   $268.3678   $268.37   $268.35   $268.40  
  Purchase #3 $148.82   13.829%   $169.4003   $169.40   $169.40   $169.40  
  Purchase #4 $109.75   7.218%   $117.6718   $117.67   $117.65   $117.70  
  Purchase #5 $233.45   5.697%   $246.7496   $246.75   $246.75   $246.70  
  Purchase #6 $127.95   7.571%   $137.6371   $137.64   $137.65   $137.60  
  Purchase #7 $47.39   6.650%   $50.5414   $50.54   $50.55   $50.50  
  7 purchase totals = $996.68       $1,082.6384   $1,082.64   $1,082.60   $1,082.60