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	$80.76	9.327%	$88.2925	$88.29	$88.30	$88.30
Purchase #2	$218.56	11.472%	$243.6332	$243.63	$243.65	$243.60
Purchase #3	$133.57	7.324%	$143.3527	$143.35	$143.35	$143.40
Purchase #4	$152.86	4.594%	$159.8824	$159.88	$159.90	$159.90
Purchase #5	$145.83	8.729%	$158.5595	$158.56	$158.55	$158.60
Purchase #6	$217.58	11.209%	$241.9685	$241.97	$241.95	$242.00
Purchase #7	$130.92	10.102%	$144.1455	$144.15	$144.15	$144.10
7 purchase totals =	$1,080.08		$1,179.8343	$1,179.83	$1,179.85	$1,179.90