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 $216.90   10.499%   $239.6723   $239.67   $239.65   $239.70  
  Purchase #2 $54.48   8.154%   $58.9223   $58.92   $58.90   $58.90  
  Purchase #3 $34.98   13.788%   $39.803   $39.80   $39.80   $39.80  
  Purchase #4 $233.32   9.783%   $256.1457   $256.15   $256.15   $256.10  
  Purchase #5 $109.40   3.181%   $112.88   $112.88   $112.90   $112.90  
  Purchase #6 $158.46   12.470%   $178.22   $178.22   $178.20   $178.20  
  Purchase #7 $75.75   7.474%   $81.4116   $81.41   $81.40   $81.40  
  7 purchase totals = $883.29       $967.0549   $967.05   $967.00   $967.00