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	$159.45	6.156%	$169.2657	$169.27	$169.25	$169.30
Purchase #2	$148.33	6.212%	$157.5443	$157.54	$157.55	$157.50
Purchase #3	$144.86	9.155%	$158.1219	$158.12	$158.10	$158.10
Purchase #4	$34.33	3.282%	$35.4567	$35.46	$35.45	$35.50
Purchase #5	$231.39	10.323%	$255.2764	$255.28	$255.30	$255.30
Purchase #6	$197.66	5.815%	$209.1539	$209.15	$209.15	$209.20
Purchase #7	$101.29	11.299%	$112.7348	$112.73	$112.75	$112.70
7 purchase totals =	$1,017.31		$1,097.5537	$1,097.55	$1,097.55	$1,097.60