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	$94.25	8.687%	$102.4375	$102.44	$102.45	$102.40
Purchase #2	$61.55	4.335%	$64.2182	$64.22	$64.20	$64.20
Purchase #3	$106.73	12.105%	$119.6497	$119.65	$119.65	$119.60
Purchase #4	$81.29	11.631%	$90.7448	$90.74	$90.75	$90.70
Purchase #5	$89.60	11.300%	$99.7248	$99.72	$99.70	$99.70
Purchase #6	$96.76	8.173%	$104.6682	$104.67	$104.65	$104.70
Purchase #7	$53.79	4.748%	$56.3439	$56.34	$56.35	$56.30
7 purchase totals =	$583.97		$637.7871	$637.78	$637.75	$637.60