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 $248.27   6.446%   $264.2735   $264.27   $264.25   $264.30  
  Purchase #2 $56.38   11.725%   $62.9906   $62.99   $63.00   $63.00  
  Purchase #3 $176.63   10.522%   $195.215   $195.22   $195.20   $195.20  
  Purchase #4 $101.83   6.543%   $108.4927   $108.49   $108.50   $108.50  
  Purchase #5 $62.97   6.866%   $67.2935   $67.29   $67.30   $67.30  
  Purchase #6 $161.83   5.475%   $170.6902   $170.69   $170.70   $170.70  
  Purchase #7 $171.84   13.689%   $195.3632   $195.36   $195.35   $195.40  
  7 purchase totals = $979.75       $1,064.3187   $1,064.31   $1,064.30   $1,064.40