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 $230.60   13.140%   $260.9008   $260.90   $260.90   $260.90  
  Purchase #2 $87.82   12.273%   $98.5981   $98.60   $98.60   $98.60  
  Purchase #3 $223.39   11.832%   $249.8215   $249.82   $249.80   $249.80  
  Purchase #4 $104.65   12.662%   $117.9008   $117.90   $117.90   $117.90  
  Purchase #5 $236.76   13.808%   $269.4518   $269.45   $269.45   $269.50  
  Purchase #6 $198.62   4.299%   $207.1587   $207.16   $207.15   $207.20  
  Purchase #7 $29.58   3.643%   $30.6576   $30.66   $30.65   $30.70  
  7 purchase totals = $1,111.42       $1,234.4893   $1,234.49   $1,234.45   $1,234.60