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	$38.77	8.753%	$42.1635	$42.16	$42.15	$42.20
Purchase #2	$139.82	6.650%	$149.118	$149.12	$149.10	$149.10
Purchase #3	$38.76	3.580%	$40.1476	$40.15	$40.15	$40.10
Purchase #4	$242.37	3.830%	$251.6528	$251.65	$251.65	$251.70
Purchase #5	$244.53	12.613%	$275.3726	$275.37	$275.35	$275.40
Purchase #6	$76.38	5.379%	$80.4885	$80.49	$80.50	$80.50
Purchase #7	$237.79	13.525%	$269.9511	$269.95	$269.95	$270.00
7 purchase totals =	$1,018.42		$1,108.8941	$1,108.89	$1,108.85	$1,109.00