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	$45.38	9.373%	$49.6335	$49.63	$49.65	$49.60
Purchase #2	$107.42	10.331%	$118.5176	$118.52	$118.50	$118.50
Purchase #3	$143.41	8.493%	$155.5898	$155.59	$155.60	$155.60
Purchase #4	$101.91	7.739%	$109.7968	$109.80	$109.80	$109.80
Purchase #5	$57.73	6.497%	$61.4807	$61.48	$61.50	$61.50
Purchase #6	$115.51	3.486%	$119.5367	$119.54	$119.55	$119.50
Purchase #7	$16.79	11.759%	$18.7643	$18.76	$18.75	$18.80
7 purchase totals =	$588.15		$633.3194	$633.32	$633.35	$633.30