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	$209.41	13.253%	$237.1631	$237.16	$237.15	$237.20
Purchase #2	$51.48	10.823%	$57.0517	$57.05	$57.05	$57.10
Purchase #3	$247.34	13.452%	$280.6122	$280.61	$280.60	$280.60
Purchase #4	$130.77	8.241%	$141.5468	$141.55	$141.55	$141.50
Purchase #5	$158.70	4.492%	$165.8288	$165.83	$165.85	$165.80
Purchase #6	$10.45	8.419%	$11.3298	$11.33	$11.35	$11.30
Purchase #7	$30.94	4.344%	$32.284	$32.28	$32.30	$32.30
7 purchase totals =	$839.09		$925.8164	$925.81	$925.85	$925.80