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 $210.98   13.520%   $239.5045   $239.50   $239.50   $239.50  
  Purchase #2 $218.31   11.769%   $244.0029   $244.00   $244.00   $244.00  
  Purchase #3 $56.31   11.822%   $62.967   $62.97   $62.95   $63.00  
  Purchase #4 $30.76   3.550%   $31.852   $31.85   $31.85   $31.90  
  Purchase #5 $195.96   11.173%   $217.8546   $217.85   $217.85   $217.90  
  Purchase #6 $136.26   10.849%   $151.0428   $151.04   $151.05   $151.00  
  Purchase #7 $11.33   5.418%   $11.9439   $11.94   $11.95   $11.90  
  7 purchase totals = $859.91       $959.1677   $959.15   $959.15   $959.20