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 $247.64   11.675%   $276.552   $276.55   $276.55   $276.60  
  Purchase #2 $125.25   8.306%   $135.6533   $135.65   $135.65   $135.70  
  Purchase #3 $131.53   11.306%   $146.4008   $146.40   $146.40   $146.40  
  Purchase #4 $245.30   11.797%   $274.238   $274.24   $274.25   $274.20  
  Purchase #5 $227.29   9.466%   $248.8053   $248.81   $248.80   $248.80  
  Purchase #6 $118.32   11.183%   $131.5517   $131.55   $131.55   $131.60  
  Purchase #7 $152.72   6.141%   $162.0985   $162.10   $162.10   $162.10  
  7 purchase totals = $1,248.05       $1,375.2996   $1,375.30   $1,375.30   $1,375.40