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 $202.91   11.543%   $226.3319   $226.33   $226.35   $226.30  
  Purchase #2 $114.77   9.559%   $125.7409   $125.74   $125.75   $125.70  
  Purchase #3 $13.48   10.363%   $14.8769   $14.88   $14.90   $14.90  
  Purchase #4 $90.26   7.782%   $97.284   $97.28   $97.30   $97.30  
  Purchase #5 $78.42   4.104%   $81.6384   $81.64   $81.65   $81.60  
  Purchase #6 $149.41   9.423%   $163.4889   $163.49   $163.50   $163.50  
  Purchase #7 $53.77   6.503%   $57.2667   $57.27   $57.25   $57.30  
  7 purchase totals = $703.02       $766.6277   $766.63   $766.70   $766.60