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	$236.81	7.732%	$255.1201	$255.12	$255.10	$255.10
Purchase #2	$49.50	13.318%	$56.0924	$56.09	$56.10	$56.10
Purchase #3	$230.92	10.709%	$255.6492	$255.65	$255.65	$255.60
Purchase #4	$131.38	9.400%	$143.7297	$143.73	$143.75	$143.70
Purchase #5	$173.84	6.778%	$185.6229	$185.62	$185.60	$185.60
Purchase #6	$80.45	9.414%	$88.0236	$88.02	$88.00	$88.00
Purchase #7	$134.63	8.375%	$145.9053	$145.91	$145.90	$145.90
7 purchase totals =	$1,037.53		$1,130.1432	$1,130.14	$1,130.10	$1,130.00