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	$73.71	11.797%	$82.4056	$82.41	$82.40	$82.40
Purchase #2	$48.94	5.387%	$51.5764	$51.58	$51.60	$51.60
Purchase #3	$116.83	9.310%	$127.7069	$127.71	$127.70	$127.70
Purchase #4	$174.90	9.590%	$191.6729	$191.67	$191.65	$191.70
Purchase #5	$83.45	12.394%	$93.7928	$93.79	$93.80	$93.80
Purchase #6	$250.42	10.150%	$275.8376	$275.84	$275.85	$275.80
Purchase #7	$159.53	4.428%	$166.594	$166.59	$166.60	$166.60
7 purchase totals =	$907.78		$989.5862	$989.59	$989.60	$989.60