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 $8.50   5.429%   $8.9615   $8.96   $8.95   $9.00  
  Purchase #2 $229.36   7.733%   $247.0964   $247.10   $247.10   $247.10  
  Purchase #3 $108.48   6.845%   $115.9055   $115.91   $115.90   $115.90  
  Purchase #4 $99.84   6.350%   $106.1798   $106.18   $106.20   $106.20  
  Purchase #5 $86.90   12.501%   $97.7634   $97.76   $97.75   $97.80  
  Purchase #6 $172.37   7.386%   $185.1012   $185.10   $185.10   $185.10  
  Purchase #7 $104.28   7.618%   $112.2241   $112.22   $112.20   $112.20  
  7 purchase totals = $809.73       $873.2319   $873.23   $873.20   $873.30