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 $116.39   8.177%   $125.9072   $125.91   $125.90   $125.90  
  Purchase #2 $57.48   13.866%   $65.4502   $65.45   $65.45   $65.50  
  Purchase #3 $26.77   9.462%   $29.303   $29.30   $29.30   $29.30  
  Purchase #4 $233.31   5.823%   $246.8956   $246.90   $246.90   $246.90  
  Purchase #5 $124.95   4.482%   $130.5503   $130.55   $130.55   $130.60  
  Purchase #6 $96.62   13.524%   $109.6869   $109.69   $109.70   $109.70  
  Purchase #7 $157.33   11.189%   $174.9337   $174.93   $174.95   $174.90  
  7 purchase totals = $812.85       $882.7269   $882.73   $882.75   $882.80