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	$30.83	11.658%	$34.4242	$34.42	$34.40	$34.40
Purchase #2	$196.59	10.612%	$217.4521	$217.45	$217.45	$217.50
Purchase #3	$86.55	4.289%	$90.2621	$90.26	$90.25	$90.30
Purchase #4	$107.71	3.249%	$111.2095	$111.21	$111.20	$111.20
Purchase #5	$242.46	12.775%	$273.4343	$273.43	$273.45	$273.40
Purchase #6	$223.42	4.181%	$232.7612	$232.76	$232.75	$232.80
Purchase #7	$11.64	9.458%	$12.7409	$12.74	$12.75	$12.70
7 purchase totals =	$899.20		$972.2843	$972.27	$972.25	$972.30