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	$35.28	11.364%	$39.2892	$39.29	$39.30	$39.30
Purchase #2	$155.38	9.612%	$170.3151	$170.32	$170.30	$170.30
Purchase #3	$61.80	4.469%	$64.5618	$64.56	$64.55	$64.60
Purchase #4	$133.93	8.708%	$145.5926	$145.59	$145.60	$145.60
Purchase #5	$38.62	12.709%	$43.5282	$43.53	$43.55	$43.50
Purchase #6	$33.35	13.285%	$37.7805	$37.78	$37.80	$37.80
Purchase #7	$149.85	3.112%	$154.5133	$154.51	$154.50	$154.50
7 purchase totals =	$608.21		$655.5807	$655.58	$655.60	$655.60