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 $206.44   9.130%   $225.288   $225.29   $225.30   $225.30  
  Purchase #2 $19.38   7.224%   $20.78   $20.78   $20.80   $20.80  
  Purchase #3 $89.27   5.247%   $93.954   $93.95   $93.95   $94.00  
  Purchase #4 $221.52   5.628%   $233.9871   $233.99   $234.00   $234.00  
  Purchase #5 $67.58   3.214%   $69.752   $69.75   $69.75   $69.80  
  Purchase #6 $132.51   4.537%   $138.522   $138.52   $138.50   $138.50  
  Purchase #7 $137.60   6.556%   $146.6211   $146.62   $146.60   $146.60  
  7 purchase totals = $874.30       $928.9042   $928.90   $928.90   $929.00