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	$101.94	6.467%	$108.5325	$108.53	$108.55	$108.50
Purchase #2	$212.55	9.487%	$232.7146	$232.71	$232.70	$232.70
Purchase #3	$61.31	8.449%	$66.4901	$66.49	$66.50	$66.50
Purchase #4	$78.63	13.406%	$89.1711	$89.17	$89.15	$89.20
Purchase #5	$15.59	10.498%	$17.2266	$17.23	$17.25	$17.20
Purchase #6	$127.96	7.307%	$137.31	$137.31	$137.30	$137.30
Purchase #7	$225.33	3.461%	$233.1287	$233.13	$233.15	$233.10
7 purchase totals =	$823.31		$884.5736	$884.57	$884.60	$884.50