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	$229.57	7.761%	$247.3869	$247.39	$247.40	$247.40
Purchase #2	$227.73	12.307%	$255.7567	$255.76	$255.75	$255.80
Purchase #3	$238.27	13.153%	$269.6097	$269.61	$269.60	$269.60
Purchase #4	$188.50	6.331%	$200.4339	$200.43	$200.45	$200.40
Purchase #5	$70.91	9.237%	$77.46	$77.46	$77.45	$77.50
Purchase #6	$40.58	7.160%	$43.4855	$43.49	$43.50	$43.50
Purchase #7	$42.68	10.452%	$47.1409	$47.14	$47.15	$47.10
7 purchase totals =	$1,038.24		$1,141.2736	$1,141.28	$1,141.30	$1,141.30