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 $230.34   12.549%   $259.2454   $259.25   $259.25   $259.20  
  Purchase #2 $199.37   6.194%   $211.719   $211.72   $211.70   $211.70  
  Purchase #3 $215.36   4.774%   $225.6413   $225.64   $225.65   $225.60  
  Purchase #4 $31.84   10.382%   $35.1456   $35.15   $35.15   $35.10  
  Purchase #5 $52.32   7.548%   $56.2691   $56.27   $56.25   $56.30  
  Purchase #6 $57.28   6.330%   $60.9058   $60.91   $60.90   $60.90  
  Purchase #7 $176.68   6.181%   $187.6006   $187.60   $187.60   $187.60  
  7 purchase totals = $963.19       $1,036.5268   $1,036.54   $1,036.50   $1,036.40