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 $206.63   8.818%   $224.8506   $224.85   $224.85   $224.90  
  Purchase #2 $211.84   8.431%   $229.7002   $229.70   $229.70   $229.70  
  Purchase #3 $157.81   4.762%   $165.3249   $165.32   $165.30   $165.30  
  Purchase #4 $15.82   7.836%   $17.0597   $17.06   $17.05   $17.10  
  Purchase #5 $82.55   13.392%   $93.6051   $93.61   $93.60   $93.60  
  Purchase #6 $129.27   5.312%   $136.1368   $136.14   $136.15   $136.10  
  Purchase #7 $91.98   6.361%   $97.8308   $97.83   $97.85   $97.80  
  7 purchase totals = $895.90       $964.5081   $964.51   $964.50   $964.50