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 $208.73   13.270%   $236.4285   $236.43   $236.45   $236.40  
  Purchase #2 $147.26   10.138%   $162.1892   $162.19   $162.20   $162.20  
  Purchase #3 $213.99   10.317%   $236.0673   $236.07   $236.05   $236.10  
  Purchase #4 $132.71   5.778%   $140.378   $140.38   $140.40   $140.40  
  Purchase #5 $47.86   9.826%   $52.5627   $52.56   $52.55   $52.60  
  Purchase #6 $116.26   11.865%   $130.0542   $130.05   $130.05   $130.10  
  Purchase #7 $33.86   5.339%   $35.6678   $35.67   $35.65   $35.70  
  7 purchase totals = $900.67       $993.3477   $993.35   $993.35   $993.50