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	$97.74	12.184%	$109.6486	$109.65	$109.65	$109.60
Purchase #2	$56.60	7.449%	$60.8161	$60.82	$60.80	$60.80
Purchase #3	$102.61	9.201%	$112.0511	$112.05	$112.05	$112.10
Purchase #4	$17.93	6.861%	$19.1602	$19.16	$19.15	$19.20
Purchase #5	$175.96	8.268%	$190.5084	$190.51	$190.50	$190.50
Purchase #6	$141.72	7.413%	$152.2257	$152.23	$152.25	$152.20
Purchase #7	$132.83	7.695%	$143.0513	$143.05	$143.05	$143.10
7 purchase totals =	$725.39		$787.4614	$787.47	$787.45	$787.50