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 $249.45   7.864%   $269.0667   $269.07   $269.05   $269.10  
  Purchase #2 $8.53   8.606%   $9.2641   $9.26   $9.25   $9.30  
  Purchase #3 $101.85   3.295%   $105.206   $105.21   $105.20   $105.20  
  Purchase #4 $88.84   5.571%   $93.7893   $93.79   $93.80   $93.80  
  Purchase #5 $86.44   13.715%   $98.2952   $98.30   $98.30   $98.30  
  Purchase #6 $20.39   6.607%   $21.7372   $21.74   $21.75   $21.70  
  Purchase #7 $247.73   5.856%   $262.2371   $262.24   $262.25   $262.20  
  7 purchase totals = $803.23       $859.5956   $859.61   $859.60   $859.60