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	$167.91	13.768%	$191.0278	$191.03	$191.05	$191.00
Purchase #2	$103.37	5.714%	$109.2766	$109.28	$109.30	$109.30
Purchase #3	$197.45	11.582%	$220.3187	$220.32	$220.30	$220.30
Purchase #4	$20.62	13.145%	$23.3305	$23.33	$23.35	$23.30
Purchase #5	$31.45	4.549%	$32.8807	$32.88	$32.90	$32.90
Purchase #6	$155.88	7.393%	$167.4042	$167.40	$167.40	$167.40
Purchase #7	$101.55	4.298%	$105.9146	$105.91	$105.90	$105.90
7 purchase totals =	$778.23		$850.1531	$850.15	$850.20	$850.10