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 $43.36   10.627%   $47.9679   $47.97   $47.95   $48.00  
  Purchase #2 $178.39   4.566%   $186.5353   $186.54   $186.55   $186.50  
  Purchase #3 $186.57   5.521%   $196.8705   $196.87   $196.85   $196.90  
  Purchase #4 $150.86   7.176%   $161.6857   $161.69   $161.70   $161.70  
  Purchase #5 $223.67   9.418%   $244.7352   $244.74   $244.75   $244.70  
  Purchase #6 $88.78   9.491%   $97.2061   $97.21   $97.20   $97.20  
  Purchase #7 $12.56   5.394%   $13.2375   $13.24   $13.25   $13.20  
  7 purchase totals = $884.19       $948.2382   $948.26   $948.25   $948.20