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	$41.26	3.867%	$42.8555	$42.86	$42.85	$42.90
Purchase #2	$33.87	5.481%	$35.7264	$35.73	$35.75	$35.70
Purchase #3	$35.45	12.747%	$39.9688	$39.97	$39.95	$40.00
Purchase #4	$157.27	10.178%	$173.2769	$173.28	$173.30	$173.30
Purchase #5	$163.65	9.635%	$179.4177	$179.42	$179.40	$179.40
Purchase #6	$119.72	6.829%	$127.8957	$127.90	$127.90	$127.90
Purchase #7	$34.34	9.814%	$37.7101	$37.71	$37.70	$37.70
7 purchase totals =	$585.56		$636.8511	$636.87	$636.85	$636.90