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 $92.86   11.250%   $103.3068   $103.31   $103.30   $103.30  
  Purchase #2 $9.90   6.199%   $10.5137   $10.51   $10.50   $10.50  
  Purchase #3 $116.61   7.535%   $125.3966   $125.40   $125.40   $125.40  
  Purchase #4 $91.38   7.203%   $97.9621   $97.96   $97.95   $98.00  
  Purchase #5 $52.30   12.855%   $59.0232   $59.02   $59.00   $59.00  
  Purchase #6 $90.87   7.416%   $97.6089   $97.61   $97.60   $97.60  
  Purchase #7 $106.88   4.797%   $112.007   $112.01   $112.00   $112.00  
  7 purchase totals = $560.80       $605.8183   $605.82   $605.75   $605.80