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	$202.66	9.352%	$221.6128	$221.61	$221.60	$221.60
Purchase #2	$135.29	6.247%	$143.7416	$143.74	$143.75	$143.70
Purchase #3	$250.94	11.121%	$278.847	$278.85	$278.85	$278.80
Purchase #4	$33.86	5.774%	$35.8151	$35.82	$35.80	$35.80
Purchase #5	$231.42	8.232%	$250.4705	$250.47	$250.45	$250.50
Purchase #6	$88.87	12.718%	$100.1725	$100.17	$100.15	$100.20
Purchase #7	$38.42	6.658%	$40.978	$40.98	$41.00	$41.00
7 purchase totals =	$981.46		$1,071.6375	$1,071.64	$1,071.60	$1,071.60