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 $228.47   8.423%   $247.714   $247.71   $247.70   $247.70  
  Purchase #2 $98.77   4.632%   $103.345   $103.35   $103.35   $103.30  
  Purchase #3 $26.38   13.418%   $29.9197   $29.92   $29.90   $29.90  
  Purchase #4 $176.78   4.221%   $184.2419   $184.24   $184.25   $184.20  
  Purchase #5 $156.63   7.577%   $168.4979   $168.50   $168.50   $168.50  
  Purchase #6 $33.29   8.614%   $36.1576   $36.16   $36.15   $36.20  
  Purchase #7 $186.29   10.507%   $205.8635   $205.86   $205.85   $205.90  
  7 purchase totals = $906.61       $975.7396   $975.74   $975.70   $975.70