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	$242.39	12.577%	$272.8754	$272.88	$272.90	$272.90
Purchase #2	$200.78	8.335%	$217.515	$217.52	$217.50	$217.50
Purchase #3	$211.47	6.798%	$225.8457	$225.85	$225.85	$225.80
Purchase #4	$25.94	12.429%	$29.1641	$29.16	$29.15	$29.20
Purchase #5	$101.54	9.441%	$111.1264	$111.13	$111.15	$111.10
Purchase #6	$88.60	11.443%	$98.7385	$98.74	$98.75	$98.70
Purchase #7	$146.94	6.471%	$156.4485	$156.45	$156.45	$156.40
7 purchase totals =	$1,017.66		$1,111.7136	$1,111.73	$1,111.75	$1,111.60