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 $90.61   5.188%   $95.3108   $95.31   $95.30   $95.30  
  Purchase #2 $92.53   6.281%   $98.3418   $98.34   $98.35   $98.30  
  Purchase #3 $243.86   9.592%   $267.2511   $267.25   $267.25   $267.30  
  Purchase #4 $109.31   12.251%   $122.7016   $122.70   $122.70   $122.70  
  Purchase #5 $24.68   8.114%   $26.6825   $26.68   $26.70   $26.70  
  Purchase #6 $225.37   7.381%   $242.0046   $242.00   $242.00   $242.00  
  Purchase #7 $75.67   8.872%   $82.3834   $82.38   $82.40   $82.40  
  7 purchase totals = $862.03       $934.6758   $934.66   $934.70   $934.70