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	$54.85	4.812%	$57.4894	$57.49	$57.50	$57.50
Purchase #2	$118.45	4.269%	$123.5066	$123.51	$123.50	$123.50
Purchase #3	$23.38	12.168%	$26.2249	$26.22	$26.20	$26.20
Purchase #4	$196.86	4.631%	$205.9766	$205.98	$206.00	$206.00
Purchase #5	$163.84	6.219%	$174.0292	$174.03	$174.05	$174.00
Purchase #6	$18.35	11.788%	$20.5131	$20.51	$20.50	$20.50
Purchase #7	$73.28	6.493%	$78.0381	$78.04	$78.05	$78.00
7 purchase totals =	$649.01		$685.7779	$685.78	$685.80	$685.70