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 $241.49   9.783%   $265.115   $265.12   $265.10   $265.10  
  Purchase #2 $172.77   9.369%   $188.9568   $188.96   $188.95   $189.00  
  Purchase #3 $93.30   5.716%   $98.633   $98.63   $98.65   $98.60  
  Purchase #4 $157.57   10.102%   $173.4877   $173.49   $173.50   $173.50  
  Purchase #5 $220.91   13.585%   $250.9206   $250.92   $250.90   $250.90  
  Purchase #6 $8.28   5.306%   $8.7193   $8.72   $8.70   $8.70  
  Purchase #7 $204.40   12.609%   $230.1728   $230.17   $230.15   $230.20  
  7 purchase totals = $1,098.72       $1,216.0052   $1,216.01   $1,215.95   $1,216.00