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 $216.67   11.697%   $242.0139   $242.01   $242.00   $242.00  
  Purchase #2 $21.30   6.706%   $22.7284   $22.73   $22.75   $22.70  
  Purchase #3 $185.33   5.726%   $195.942   $195.94   $195.95   $195.90  
  Purchase #4 $26.95   13.137%   $30.4904   $30.49   $30.50   $30.50  
  Purchase #5 $245.88   8.265%   $266.202   $266.20   $266.20   $266.20  
  Purchase #6 $211.47   6.562%   $225.3467   $225.35   $225.35   $225.30  
  Purchase #7 $8.66   6.607%   $9.2322   $9.23   $9.25   $9.20  
  7 purchase totals = $916.26       $991.9556   $991.95   $992.00   $991.80