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 $212.30   11.154%   $235.9799   $235.98   $236.00   $236.00  
  Purchase #2 $224.95   3.703%   $233.2799   $233.28   $233.30   $233.30  
  Purchase #3 $208.89   11.509%   $232.9312   $232.93   $232.95   $232.90  
  Purchase #4 $173.44   13.508%   $196.8683   $196.87   $196.85   $196.90  
  Purchase #5 $191.29   12.667%   $215.5207   $215.52   $215.50   $215.50  
  Purchase #6 $93.49   5.512%   $98.6432   $98.64   $98.65   $98.60  
  Purchase #7 $219.63   11.395%   $244.6568   $244.66   $244.65   $244.70  
  7 purchase totals = $1,323.99       $1,457.8800   $1,457.88   $1,457.90   $1,457.90