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	$221.37	10.578%	$244.7865	$244.79	$244.80	$244.80
Purchase #2	$151.71	13.545%	$172.2591	$172.26	$172.25	$172.30
Purchase #3	$247.72	9.757%	$271.89	$271.89	$271.90	$271.90
Purchase #4	$79.89	13.224%	$90.4547	$90.45	$90.45	$90.50
Purchase #5	$101.70	6.854%	$108.6705	$108.67	$108.65	$108.70
Purchase #6	$248.88	6.708%	$265.5749	$265.57	$265.55	$265.60
Purchase #7	$51.82	12.728%	$58.4156	$58.42	$58.40	$58.40
7 purchase totals =	$1,103.09		$1,212.0513	$1,212.05	$1,212.00	$1,212.20