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 $246.32   11.348%   $274.2724   $274.27   $274.25   $274.30  
  Purchase #2 $76.75   10.619%   $84.9001   $84.90   $84.90   $84.90  
  Purchase #3 $58.71   6.544%   $62.552   $62.55   $62.55   $62.60  
  Purchase #4 $227.90   3.105%   $234.9763   $234.98   $235.00   $235.00  
  Purchase #5 $131.75   11.424%   $146.8011   $146.80   $146.80   $146.80  
  Purchase #6 $183.29   12.533%   $206.2617   $206.26   $206.25   $206.30  
  Purchase #7 $114.41   5.199%   $120.3582   $120.36   $120.35   $120.40  
  7 purchase totals = $1,039.13       $1,130.1218   $1,130.12   $1,130.10   $1,130.30