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 $55.47   11.293%   $61.7342   $61.73   $61.75   $61.70  
  Purchase #2 $21.99   4.388%   $22.9549   $22.95   $22.95   $23.00  
  Purchase #3 $223.71   11.657%   $249.7879   $249.79   $249.80   $249.80  
  Purchase #4 $12.29   9.538%   $13.4622   $13.46   $13.45   $13.50  
  Purchase #5 $117.71   10.499%   $130.0684   $130.07   $130.05   $130.10  
  Purchase #6 $173.84   6.817%   $185.6907   $185.69   $185.70   $185.70  
  Purchase #7 $14.87   7.522%   $15.9885   $15.99   $16.00   $16.00  
  7 purchase totals = $619.88       $679.6868   $679.68   $679.70   $679.80