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 $206.91   9.307%   $226.1671   $226.17   $226.15   $226.20  
  Purchase #2 $226.99   3.492%   $234.9165   $234.92   $234.90   $234.90  
  Purchase #3 $22.78   13.826%   $25.9296   $25.93   $25.95   $25.90  
  Purchase #4 $55.61   10.169%   $61.265   $61.27   $61.25   $61.30  
  Purchase #5 $186.72   3.339%   $192.9546   $192.95   $192.95   $193.00  
  Purchase #6 $87.60   5.528%   $92.4425   $92.44   $92.45   $92.40  
  Purchase #7 $169.93   9.845%   $186.6596   $186.66   $186.65   $186.70  
  7 purchase totals = $956.54       $1,020.3349   $1,020.34   $1,020.30   $1,020.40