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 $54.94   7.238%   $58.9166   $58.92   $58.90   $58.90  
  Purchase #2 $56.31   10.535%   $62.2423   $62.24   $62.25   $62.20  
  Purchase #3 $132.68   7.707%   $142.9056   $142.91   $142.90   $142.90  
  Purchase #4 $13.63   5.544%   $14.3856   $14.39   $14.40   $14.40  
  Purchase #5 $55.72   10.517%   $61.5801   $61.58   $61.60   $61.60  
  Purchase #6 $84.59   11.451%   $94.2764   $94.28   $94.30   $94.30  
  Purchase #7 $34.47   6.305%   $36.6433   $36.64   $36.65   $36.60  
  7 purchase totals = $432.34       $470.9499   $470.96   $471.00   $470.90