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	$96.56	4.176%	$100.5923	$100.59	$100.60	$100.60
Purchase #2	$114.67	13.635%	$130.3053	$130.31	$130.30	$130.30
Purchase #3	$123.27	7.585%	$132.62	$132.62	$132.60	$132.60
Purchase #4	$191.32	12.522%	$215.2771	$215.28	$215.30	$215.30
Purchase #5	$202.45	9.724%	$222.1362	$222.14	$222.15	$222.10
Purchase #6	$128.60	11.251%	$143.0688	$143.07	$143.05	$143.10
Purchase #7	$202.74	13.377%	$229.8605	$229.86	$229.85	$229.90
7 purchase totals =	$1,059.61		$1,173.8602	$1,173.87	$1,173.85	$1,173.90