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	$64.43	10.307%	$71.0708	$71.07	$71.05	$71.10
Purchase #2	$241.30	6.227%	$256.3258	$256.33	$256.35	$256.30
Purchase #3	$56.91	3.533%	$58.9206	$58.92	$58.90	$58.90
Purchase #4	$13.26	3.417%	$13.7131	$13.71	$13.70	$13.70
Purchase #5	$33.91	9.786%	$37.2284	$37.23	$37.25	$37.20
Purchase #6	$25.52	7.575%	$27.4531	$27.45	$27.45	$27.50
Purchase #7	$154.27	12.228%	$173.1341	$173.13	$173.15	$173.10
7 purchase totals =	$589.60		$637.8459	$637.84	$637.85	$637.80