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 $85.86   8.602%   $93.2457   $93.25   $93.25   $93.20  
  Purchase #2 $62.68   5.472%   $66.1098   $66.11   $66.10   $66.10  
  Purchase #3 $217.60   6.575%   $231.9072   $231.91   $231.90   $231.90  
  Purchase #4 $12.34   5.193%   $12.9808   $12.98   $13.00   $13.00  
  Purchase #5 $112.76   10.145%   $124.1995   $124.20   $124.20   $124.20  
  Purchase #6 $57.34   10.646%   $63.4444   $63.44   $63.45   $63.40  
  Purchase #7 $66.64   3.477%   $68.9571   $68.96   $68.95   $69.00  
  7 purchase totals = $615.22       $660.8445   $660.85   $660.85   $660.80