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 $88.63   8.555%   $96.2123   $96.21   $96.20   $96.20  
  Purchase #2 $23.77   11.440%   $26.4893   $26.49   $26.50   $26.50  
  Purchase #3 $202.96   9.323%   $221.882   $221.88   $221.90   $221.90  
  Purchase #4 $242.97   12.805%   $274.0823   $274.08   $274.10   $274.10  
  Purchase #5 $54.61   10.612%   $60.4052   $60.41   $60.40   $60.40  
  Purchase #6 $227.43   11.806%   $254.2804   $254.28   $254.30   $254.30  
  Purchase #7 $233.26   5.296%   $245.6134   $245.61   $245.60   $245.60  
  7 purchase totals = $1,073.63       $1,178.9649   $1,178.96   $1,179.00   $1,179.00