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 $241.45   8.829%   $262.7676   $262.77   $262.75   $262.80  
  Purchase #2 $73.96   13.234%   $83.7479   $83.75   $83.75   $83.70  
  Purchase #3 $71.86   13.698%   $81.7034   $81.70   $81.70   $81.70  
  Purchase #4 $24.64   6.610%   $26.2687   $26.27   $26.25   $26.30  
  Purchase #5 $148.74   5.662%   $157.1617   $157.16   $157.15   $157.20  
  Purchase #6 $10.48   7.188%   $11.2333   $11.23   $11.25   $11.20  
  Purchase #7 $29.98   12.622%   $33.7641   $33.76   $33.75   $33.80  
  7 purchase totals = $601.11       $656.6467   $656.64   $656.60   $656.70