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	$90.71	10.674%	$100.3924	$100.39	$100.40	$100.40
Purchase #2	$80.70	8.846%	$87.8387	$87.84	$87.85	$87.80
Purchase #3	$76.91	13.769%	$87.4997	$87.50	$87.50	$87.50
Purchase #4	$117.54	8.538%	$127.5756	$127.58	$127.60	$127.60
Purchase #5	$129.95	6.547%	$138.4578	$138.46	$138.45	$138.50
Purchase #6	$248.82	7.800%	$268.228	$268.23	$268.25	$268.20
Purchase #7	$210.31	4.862%	$220.5353	$220.54	$220.55	$220.50
7 purchase totals =	$954.94		$1,030.5275	$1,030.54	$1,030.60	$1,030.50