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 $248.70   8.528%   $269.9091   $269.91   $269.90   $269.90  
  Purchase #2 $129.76   11.329%   $144.4605   $144.46   $144.45   $144.50  
  Purchase #3 $43.69   8.274%   $47.3049   $47.30   $47.30   $47.30  
  Purchase #4 $154.53   8.656%   $167.9061   $167.91   $167.90   $167.90  
  Purchase #5 $188.35   3.163%   $194.3075   $194.31   $194.30   $194.30  
  Purchase #6 $245.51   4.501%   $256.5604   $256.56   $256.55   $256.60  
  Purchase #7 $102.33   7.797%   $110.3087   $110.31   $110.30   $110.30  
  7 purchase totals = $1,112.87       $1,190.7572   $1,190.76   $1,190.70   $1,190.80