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	$85.58	9.375%	$93.6031	$93.60	$93.60	$93.60
Purchase #2	$52.69	11.590%	$58.7968	$58.80	$58.80	$58.80
Purchase #3	$250.74	11.486%	$279.54	$279.54	$279.55	$279.50
Purchase #4	$118.44	3.132%	$122.1495	$122.15	$122.15	$122.10
Purchase #5	$193.45	8.140%	$209.1968	$209.20	$209.20	$209.20
Purchase #6	$80.72	10.742%	$89.3909	$89.39	$89.40	$89.40
Purchase #7	$199.52	4.486%	$208.4705	$208.47	$208.45	$208.50
7 purchase totals =	$981.14		$1,061.1476	$1,061.15	$1,061.15	$1,061.10