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 $105.58   13.607%   $119.9463   $119.95   $119.95   $119.90  
  Purchase #2 $164.54   11.176%   $182.929   $182.93   $182.95   $182.90  
  Purchase #3 $104.38   9.481%   $114.2763   $114.28   $114.30   $114.30  
  Purchase #4 $66.50   13.717%   $75.6218   $75.62   $75.60   $75.60  
  Purchase #5 $149.86   9.534%   $164.1477   $164.15   $164.15   $164.10  
  Purchase #6 $208.46   11.739%   $232.9311   $232.93   $232.95   $232.90  
  Purchase #7 $146.56   10.747%   $162.3108   $162.31   $162.30   $162.30  
  7 purchase totals = $945.88       $1,052.1630   $1,052.17   $1,052.20   $1,052.00