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 $62.90   12.506%   $70.7663   $70.77   $70.75   $70.80  
  Purchase #2 $233.41   6.375%   $248.2899   $248.29   $248.30   $248.30  
  Purchase #3 $236.75   9.247%   $258.6423   $258.64   $258.65   $258.60  
  Purchase #4 $167.63   10.213%   $184.7501   $184.75   $184.75   $184.80  
  Purchase #5 $193.74   8.404%   $210.0219   $210.02   $210.00   $210.00  
  Purchase #6 $223.56   11.601%   $249.4952   $249.50   $249.50   $249.50  
  Purchase #7 $220.38   6.704%   $235.1543   $235.15   $235.15   $235.20  
  7 purchase totals = $1,338.37       $1,457.1200   $1,457.12   $1,457.10   $1,457.20