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 $209.73   8.339%   $227.2194   $227.22   $227.20   $227.20  
  Purchase #2 $183.38   10.743%   $203.0805   $203.08   $203.10   $203.10  
  Purchase #3 $151.75   11.654%   $169.4349   $169.43   $169.45   $169.40  
  Purchase #4 $234.73   13.697%   $266.881   $266.88   $266.90   $266.90  
  Purchase #5 $113.44   6.491%   $120.8034   $120.80   $120.80   $120.80  
  Purchase #6 $219.80   13.616%   $249.728   $249.73   $249.75   $249.70  
  Purchase #7 $105.40   8.747%   $114.6193   $114.62   $114.60   $114.60  
  7 purchase totals = $1,218.23       $1,351.7665   $1,351.76   $1,351.80   $1,351.70