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 $212.44   10.491%   $234.7271   $234.73   $234.75   $234.70  
  Purchase #2 $71.85   8.345%   $77.8459   $77.85   $77.85   $77.80  
  Purchase #3 $11.29   10.778%   $12.5068   $12.51   $12.50   $12.50  
  Purchase #4 $42.30   8.759%   $46.0051   $46.01   $46.00   $46.00  
  Purchase #5 $158.68   3.240%   $163.8212   $163.82   $163.80   $163.80  
  Purchase #6 $165.37   5.393%   $174.2884   $174.29   $174.30   $174.30  
  Purchase #7 $221.46   8.152%   $239.5134   $239.51   $239.50   $239.50  
  7 purchase totals = $883.39       $948.7079   $948.72   $948.70   $948.60