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	$236.72	3.187%	$244.2643	$244.26	$244.25	$244.30
Purchase #2	$135.50	4.736%	$141.9173	$141.92	$141.90	$141.90
Purchase #3	$28.82	13.640%	$32.751	$32.75	$32.75	$32.80
Purchase #4	$32.47	7.273%	$34.8315	$34.83	$34.85	$34.80
Purchase #5	$16.87	9.384%	$18.4531	$18.45	$18.45	$18.50
Purchase #6	$87.63	13.124%	$99.1306	$99.13	$99.15	$99.10
Purchase #7	$17.97	13.178%	$20.3381	$20.34	$20.35	$20.30
7 purchase totals =	$555.98		$591.6859	$591.68	$591.70	$591.70