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	$143.30	10.610%	$158.5041	$158.50	$158.50	$158.50
Purchase #2	$83.79	5.532%	$88.4253	$88.43	$88.45	$88.40
Purchase #3	$156.85	12.470%	$176.4092	$176.41	$176.40	$176.40
Purchase #4	$109.91	4.309%	$114.646	$114.65	$114.65	$114.60
Purchase #5	$200.72	13.559%	$227.9356	$227.94	$227.95	$227.90
Purchase #6	$230.46	10.169%	$253.8955	$253.90	$253.90	$253.90
Purchase #7	$141.44	4.715%	$148.1089	$148.11	$148.10	$148.10
7 purchase totals =	$1,066.47		$1,167.9246	$1,167.94	$1,167.95	$1,167.80