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 $243.55   9.191%   $265.9347   $265.93   $265.95   $265.90  
  Purchase #2 $223.33   11.672%   $249.3971   $249.40   $249.40   $249.40  
  Purchase #3 $11.96   3.583%   $12.3885   $12.39   $12.40   $12.40  
  Purchase #4 $113.78   3.153%   $117.3675   $117.37   $117.35   $117.40  
  Purchase #5 $20.49   5.117%   $21.5385   $21.54   $21.55   $21.50  
  Purchase #6 $206.29   8.577%   $223.9835   $223.98   $224.00   $224.00  
  Purchase #7 $168.87   9.709%   $185.2656   $185.27   $185.25   $185.30  
  7 purchase totals = $988.27       $1,075.8754   $1,075.88   $1,075.90   $1,075.90