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 $207.38   9.199%   $226.4569   $226.46   $226.45   $226.50  
  Purchase #2 $172.64   8.236%   $186.8586   $186.86   $186.85   $186.90  
  Purchase #3 $88.97   3.195%   $91.8126   $91.81   $91.80   $91.80  
  Purchase #4 $12.79   5.252%   $13.4617   $13.46   $13.45   $13.50  
  Purchase #5 $216.31   8.131%   $233.8982   $233.90   $233.90   $233.90  
  Purchase #6 $247.73   11.594%   $276.4518   $276.45   $276.45   $276.50  
  Purchase #7 $127.66   4.423%   $133.3064   $133.31   $133.30   $133.30  
  7 purchase totals = $1,073.48       $1,162.2462   $1,162.25   $1,162.20   $1,162.40