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	$79.25	11.217%	$88.1395	$88.14	$88.15	$88.10
Purchase #2	$86.58	3.464%	$89.5791	$89.58	$89.60	$89.60
Purchase #3	$171.33	10.103%	$188.6395	$188.64	$188.65	$188.60
Purchase #4	$141.71	11.329%	$157.7643	$157.76	$157.75	$157.80
Purchase #5	$73.49	5.480%	$77.5173	$77.52	$77.50	$77.50
Purchase #6	$173.79	6.179%	$184.5285	$184.53	$184.55	$184.50
Purchase #7	$116.29	8.405%	$126.0642	$126.06	$126.05	$126.10
7 purchase totals =	$842.44		$912.2324	$912.23	$912.25	$912.20