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	$18.78	6.364%	$19.9752	$19.98	$20.00	$20.00
Purchase #2	$6.88	7.708%	$7.4103	$7.41	$7.40	$7.40
Purchase #3	$241.75	10.559%	$267.2764	$267.28	$267.30	$267.30
Purchase #4	$55.94	11.412%	$62.3239	$62.32	$62.30	$62.30
Purchase #5	$131.41	12.679%	$148.0715	$148.07	$148.05	$148.10
Purchase #6	$72.76	13.232%	$82.3876	$82.39	$82.40	$82.40
Purchase #7	$34.37	3.298%	$35.5035	$35.50	$35.50	$35.50
7 purchase totals =	$561.89		$622.9484	$622.95	$622.95	$623.00