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 $208.44   13.359%   $236.2855   $236.29   $236.30   $236.30  
  Purchase #2 $24.58   9.469%   $26.9075   $26.91   $26.90   $26.90  
  Purchase #3 $29.33   11.429%   $32.6821   $32.68   $32.70   $32.70  
  Purchase #4 $141.59   9.683%   $155.3002   $155.30   $155.30   $155.30  
  Purchase #5 $143.43   11.153%   $159.4267   $159.43   $159.45   $159.40  
  Purchase #6 $158.51   7.344%   $170.151   $170.15   $170.15   $170.20  
  Purchase #7 $176.47   3.273%   $182.2459   $182.25   $182.25   $182.20  
  7 purchase totals = $882.35       $962.9989   $963.01   $963.05   $963.00