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 $249.37   10.760%   $276.2022   $276.20   $276.20   $276.20  
  Purchase #2 $88.78   3.168%   $91.5926   $91.59   $91.60   $91.60  
  Purchase #3 $208.31   4.672%   $218.0422   $218.04   $218.05   $218.00  
  Purchase #4 $107.37   11.112%   $119.301   $119.30   $119.30   $119.30  
  Purchase #5 $92.50   13.714%   $105.1855   $105.19   $105.20   $105.20  
  Purchase #6 $185.68   9.773%   $203.8265   $203.83   $203.85   $203.80  
  Purchase #7 $151.67   4.425%   $158.3814   $158.38   $158.40   $158.40  
  7 purchase totals = $1,083.68       $1,172.5314   $1,172.53   $1,172.60   $1,172.50