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 $66.38   11.836%   $74.2367   $74.24   $74.25   $74.20  
  Purchase #2 $213.29   10.295%   $235.2482   $235.25   $235.25   $235.20  
  Purchase #3 $204.59   4.622%   $214.0461   $214.05   $214.05   $214.00  
  Purchase #4 $227.76   8.315%   $246.6982   $246.70   $246.70   $246.70  
  Purchase #5 $58.64   7.210%   $62.8679   $62.87   $62.85   $62.90  
  Purchase #6 $90.35   11.788%   $101.0005   $101.00   $101.00   $101.00  
  Purchase #7 $86.92   12.188%   $97.5138   $97.51   $97.50   $97.50  
  7 purchase totals = $947.93       $1,031.6114   $1,031.62   $1,031.60   $1,031.50