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	$63.89	11.494%	$71.2335	$71.23	$71.25	$71.20
Purchase #2	$93.71	7.108%	$100.3709	$100.37	$100.35	$100.40
Purchase #3	$208.52	10.389%	$230.1831	$230.18	$230.20	$230.20
Purchase #4	$93.53	6.260%	$99.385	$99.39	$99.40	$99.40
Purchase #5	$102.28	8.805%	$111.2858	$111.29	$111.30	$111.30
Purchase #6	$104.89	13.141%	$118.6736	$118.67	$118.65	$118.70
Purchase #7	$230.38	11.192%	$256.1641	$256.16	$256.15	$256.20
7 purchase totals =	$897.20		$987.2960	$987.29	$987.30	$987.40