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	$151.78	4.613%	$158.7816	$158.78	$158.80	$158.80
Purchase #2	$208.67	6.138%	$221.4782	$221.48	$221.50	$221.50
Purchase #3	$33.49	5.841%	$35.4462	$35.45	$35.45	$35.40
Purchase #4	$25.70	12.422%	$28.8925	$28.89	$28.90	$28.90
Purchase #5	$121.95	7.528%	$131.1304	$131.13	$131.15	$131.10
Purchase #6	$140.95	7.176%	$151.0646	$151.06	$151.05	$151.10
Purchase #7	$87.56	11.310%	$97.463	$97.46	$97.45	$97.50
7 purchase totals =	$770.10		$824.2565	$824.25	$824.30	$824.30