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	$29.29	13.139%	$33.1384	$33.14	$33.15	$33.10
Purchase #2	$178.79	5.859%	$189.2653	$189.27	$189.25	$189.30
Purchase #3	$100.42	11.293%	$111.7604	$111.76	$111.75	$111.80
Purchase #4	$147.72	3.853%	$153.4117	$153.41	$153.40	$153.40
Purchase #5	$205.66	9.710%	$225.6296	$225.63	$225.65	$225.60
Purchase #6	$75.97	4.131%	$79.1083	$79.11	$79.10	$79.10
Purchase #7	$213.53	4.287%	$222.684	$222.68	$222.70	$222.70
7 purchase totals =	$951.38		$1,014.9977	$1,015.00	$1,015.00	$1,015.00