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 $32.49   11.451%   $36.2104   $36.21   $36.20   $36.20  
  Purchase #2 $167.99   3.245%   $173.4413   $173.44   $173.45   $173.40  
  Purchase #3 $153.85   9.434%   $168.3642   $168.36   $168.35   $168.40  
  Purchase #4 $132.62   12.585%   $149.3102   $149.31   $149.30   $149.30  
  Purchase #5 $48.78   4.680%   $51.0629   $51.06   $51.05   $51.10  
  Purchase #6 $105.54   10.850%   $116.9911   $116.99   $117.00   $117.00  
  Purchase #7 $240.87   4.725%   $252.2511   $252.25   $252.25   $252.30  
  7 purchase totals = $882.14       $947.6312   $947.62   $947.60   $947.70