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	$75.53	4.124%	$78.6449	$78.64	$78.65	$78.60
Purchase #2	$237.53	13.858%	$270.4469	$270.45	$270.45	$270.40
Purchase #3	$55.94	8.251%	$60.5556	$60.56	$60.55	$60.60
Purchase #4	$155.58	5.513%	$164.1571	$164.16	$164.15	$164.20
Purchase #5	$73.85	11.209%	$82.1278	$82.13	$82.15	$82.10
Purchase #6	$240.95	10.669%	$266.657	$266.66	$266.65	$266.70
Purchase #7	$150.80	9.742%	$165.4909	$165.49	$165.50	$165.50
7 purchase totals =	$990.18		$1,088.0802	$1,088.09	$1,088.10	$1,088.10