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 $239.63   12.275%   $269.0446   $269.04   $269.05   $269.00  
  Purchase #2 $91.43   7.523%   $98.3083   $98.31   $98.30   $98.30  
  Purchase #3 $82.76   13.442%   $93.8846   $93.88   $93.90   $93.90  
  Purchase #4 $224.97   7.420%   $241.6628   $241.66   $241.65   $241.70  
  Purchase #5 $19.35   6.140%   $20.5381   $20.54   $20.55   $20.50  
  Purchase #6 $220.73   3.119%   $227.6146   $227.61   $227.60   $227.60  
  Purchase #7 $191.59   12.616%   $215.761   $215.76   $215.75   $215.80  
  7 purchase totals = $1,070.46       $1,166.8140   $1,166.80   $1,166.80   $1,166.80