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 $35.61   6.752%   $38.0144   $38.01   $38.00   $38.00  
  Purchase #2 $54.99   10.734%   $60.8926   $60.89   $60.90   $60.90  
  Purchase #3 $93.59   10.848%   $103.7426   $103.74   $103.75   $103.70  
  Purchase #4 $247.43   4.182%   $257.7775   $257.78   $257.80   $257.80  
  Purchase #5 $141.45   7.812%   $152.5001   $152.50   $152.50   $152.50  
  Purchase #6 $173.89   4.646%   $181.9689   $181.97   $181.95   $182.00  
  Purchase #7 $158.51   12.460%   $178.2603   $178.26   $178.25   $178.30  
  7 purchase totals = $905.47       $973.1564   $973.15   $973.15   $973.20