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 $214.99   10.334%   $237.2071   $237.21   $237.20   $237.20  
  Purchase #2 $94.88   4.245%   $98.9077   $98.91   $98.90   $98.90  
  Purchase #3 $42.38   5.204%   $44.5855   $44.59   $44.60   $44.60  
  Purchase #4 $12.95   5.453%   $13.6562   $13.66   $13.65   $13.70  
  Purchase #5 $54.65   7.269%   $58.6225   $58.62   $58.60   $58.60  
  Purchase #6 $234.42   6.695%   $250.1144   $250.11   $250.10   $250.10  
  Purchase #7 $230.75   9.180%   $251.9329   $251.93   $251.95   $251.90  
  7 purchase totals = $885.02       $955.0263   $955.03   $955.00   $955.00