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 $64.93   12.765%   $73.2183   $73.22   $73.20   $73.20  
  Purchase #2 $39.41   5.198%   $41.4585   $41.46   $41.45   $41.50  
  Purchase #3 $46.36   7.344%   $49.7647   $49.76   $49.75   $49.80  
  Purchase #4 $179.83   8.521%   $195.1533   $195.15   $195.15   $195.20  
  Purchase #5 $214.97   11.457%   $239.5991   $239.60   $239.60   $239.60  
  Purchase #6 $60.71   6.622%   $64.7302   $64.73   $64.75   $64.70  
  Purchase #7 $229.73   7.596%   $247.1803   $247.18   $247.20   $247.20  
  7 purchase totals = $835.94       $911.1044   $911.10   $911.10   $911.20