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 $83.82   10.268%   $92.4266   $92.43   $92.45   $92.40  
  Purchase #2 $247.50   13.870%   $281.8283   $281.83   $281.85   $281.80  
  Purchase #3 $187.64   9.660%   $205.766   $205.77   $205.75   $205.80  
  Purchase #4 $231.37   4.681%   $242.2004   $242.20   $242.20   $242.20  
  Purchase #5 $155.26   3.868%   $161.2655   $161.27   $161.25   $161.30  
  Purchase #6 $146.46   4.210%   $152.626   $152.63   $152.65   $152.60  
  Purchase #7 $118.39   13.113%   $133.9145   $133.91   $133.90   $133.90  
  7 purchase totals = $1,170.44       $1,270.0273   $1,270.04   $1,270.05   $1,270.00