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 $241.91   8.308%   $262.0079   $262.01   $262.00   $262.00  
  Purchase #2 $51.97   3.175%   $53.62   $53.62   $53.60   $53.60  
  Purchase #3 $205.57   5.642%   $217.1683   $217.17   $217.15   $217.20  
  Purchase #4 $129.84   8.282%   $140.5933   $140.59   $140.60   $140.60  
  Purchase #5 $27.95   7.357%   $30.0063   $30.01   $30.00   $30.00  
  Purchase #6 $126.61   4.299%   $132.053   $132.05   $132.05   $132.10  
  Purchase #7 $142.98   10.415%   $157.8714   $157.87   $157.85   $157.90  
  7 purchase totals = $926.83       $993.3202   $993.32   $993.25   $993.40