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 $88.32   8.738%   $96.0374   $96.04   $96.05   $96.00  
  Purchase #2 $157.63   7.439%   $169.3561   $169.36   $169.35   $169.40  
  Purchase #3 $194.88   5.504%   $205.6062   $205.61   $205.60   $205.60  
  Purchase #4 $190.82   11.757%   $213.2547   $213.25   $213.25   $213.30  
  Purchase #5 $26.34   3.766%   $27.332   $27.33   $27.35   $27.30  
  Purchase #6 $242.27   7.116%   $259.5099   $259.51   $259.50   $259.50  
  Purchase #7 $22.54   3.821%   $23.4013   $23.40   $23.40   $23.40  
  7 purchase totals = $922.80       $994.4976   $994.50   $994.50   $994.50