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 $228.98   8.731%   $248.9722   $248.97   $248.95   $249.00  
  Purchase #2 $20.56   10.727%   $22.7655   $22.77   $22.75   $22.80  
  Purchase #3 $239.88   7.289%   $257.3649   $257.36   $257.35   $257.40  
  Purchase #4 $89.78   8.502%   $97.4131   $97.41   $97.40   $97.40  
  Purchase #5 $242.97   8.561%   $263.7707   $263.77   $263.75   $263.80  
  Purchase #6 $167.34   9.583%   $183.3762   $183.38   $183.40   $183.40  
  Purchase #7 $84.80   10.177%   $93.4301   $93.43   $93.45   $93.40  
  7 purchase totals = $1,074.31       $1,167.0927   $1,167.09   $1,167.05   $1,167.20