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 $121.47   3.454%   $125.6656   $125.67   $125.65   $125.70  
  Purchase #2 $222.66   11.641%   $248.5799   $248.58   $248.60   $248.60  
  Purchase #3 $233.42   6.758%   $249.1945   $249.19   $249.20   $249.20  
  Purchase #4 $167.33   13.843%   $190.4935   $190.49   $190.50   $190.50  
  Purchase #5 $225.35   6.761%   $240.5859   $240.59   $240.60   $240.60  
  Purchase #6 $166.54   5.252%   $175.2867   $175.29   $175.30   $175.30  
  Purchase #7 $187.69   3.829%   $194.8767   $194.88   $194.90   $194.90  
  7 purchase totals = $1,324.46       $1,424.6828   $1,424.69   $1,424.75   $1,424.80