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 $168.62   9.218%   $184.1634   $184.16   $184.15   $184.20  
  Purchase #2 $84.62   13.526%   $96.0657   $96.07   $96.05   $96.10  
  Purchase #3 $35.55   3.869%   $36.9254   $36.93   $36.95   $36.90  
  Purchase #4 $118.42   9.252%   $129.3762   $129.38   $129.40   $129.40  
  Purchase #5 $173.91   6.300%   $184.8663   $184.87   $184.85   $184.90  
  Purchase #6 $155.48   13.743%   $176.8476   $176.85   $176.85   $176.80  
  Purchase #7 $107.54   11.804%   $120.234   $120.23   $120.25   $120.20  
  7 purchase totals = $844.14       $928.4786   $928.49   $928.50   $928.50