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 $87.85   12.527%   $98.855   $98.86   $98.85   $98.90  
  Purchase #2 $183.82   4.828%   $192.6948   $192.69   $192.70   $192.70  
  Purchase #3 $221.93   9.415%   $242.8247   $242.82   $242.80   $242.80  
  Purchase #4 $154.30   3.289%   $159.3749   $159.37   $159.35   $159.40  
  Purchase #5 $141.98   5.768%   $150.1694   $150.17   $150.15   $150.20  
  Purchase #6 $82.44   5.242%   $86.7615   $86.76   $86.75   $86.80  
  Purchase #7 $151.31   7.528%   $162.7006   $162.70   $162.70   $162.70  
  7 purchase totals = $1,023.63       $1,093.3809   $1,093.37   $1,093.30   $1,093.50