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 $161.95   13.860%   $184.3963   $184.40   $184.40   $184.40  
  Purchase #2 $31.54   13.141%   $35.6847   $35.68   $35.70   $35.70  
  Purchase #3 $168.29   7.111%   $180.2571   $180.26   $180.25   $180.30  
  Purchase #4 $158.77   12.383%   $178.4305   $178.43   $178.45   $178.40  
  Purchase #5 $101.34   8.737%   $110.1941   $110.19   $110.20   $110.20  
  Purchase #6 $11.65   3.214%   $12.0244   $12.02   $12.00   $12.00  
  Purchase #7 $92.93   9.376%   $101.6431   $101.64   $101.65   $101.60  
  7 purchase totals = $726.47       $802.6302   $802.62   $802.65   $802.60