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	$198.38	7.318%	$212.8974	$212.90	$212.90	$212.90
Purchase #2	$148.42	7.539%	$159.6094	$159.61	$159.60	$159.60
Purchase #3	$83.71	6.376%	$89.0473	$89.05	$89.05	$89.00
Purchase #4	$247.80	9.463%	$271.2493	$271.25	$271.25	$271.20
Purchase #5	$25.79	11.540%	$28.7662	$28.77	$28.75	$28.80
Purchase #6	$234.25	13.757%	$266.4758	$266.48	$266.50	$266.50
Purchase #7	$99.55	10.321%	$109.8246	$109.82	$109.80	$109.80
7 purchase totals =	$1,037.90		$1,137.8700	$1,137.88	$1,137.85	$1,137.80