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 $213.27   13.857%   $242.8228   $242.82   $242.80   $242.80  
  Purchase #2 $246.94   11.104%   $274.3602   $274.36   $274.35   $274.40  
  Purchase #3 $211.55   4.244%   $220.5282   $220.53   $220.55   $220.50  
  Purchase #4 $86.30   12.498%   $97.0858   $97.09   $97.10   $97.10  
  Purchase #5 $231.26   4.279%   $241.1556   $241.16   $241.15   $241.20  
  Purchase #6 $159.49   8.587%   $173.1854   $173.19   $173.20   $173.20  
  Purchase #7 $57.95   13.791%   $65.9419   $65.94   $65.95   $65.90  
  7 purchase totals = $1,206.76       $1,315.0799   $1,315.09   $1,315.10   $1,315.10