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 $83.39   12.643%   $93.933   $93.93   $93.95   $93.90  
  Purchase #2 $57.66   6.831%   $61.5988   $61.60   $61.60   $61.60  
  Purchase #3 $244.25   13.104%   $276.2565   $276.26   $276.25   $276.30  
  Purchase #4 $214.40   13.662%   $243.6913   $243.69   $243.70   $243.70  
  Purchase #5 $28.39   12.112%   $31.8286   $31.83   $31.85   $31.80  
  Purchase #6 $140.91   12.751%   $158.8774   $158.88   $158.90   $158.90  
  Purchase #7 $90.87   7.298%   $97.5017   $97.50   $97.50   $97.50  
  7 purchase totals = $859.87       $963.6873   $963.69   $963.75   $963.70