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	$167.87	8.258%	$181.7327	$181.73	$181.75	$181.70
Purchase #2	$130.41	6.286%	$138.6076	$138.61	$138.60	$138.60
Purchase #3	$196.99	13.420%	$223.4261	$223.43	$223.45	$223.40
Purchase #4	$65.28	7.870%	$70.4175	$70.42	$70.40	$70.40
Purchase #5	$91.44	9.837%	$100.435	$100.44	$100.45	$100.40
Purchase #6	$48.83	11.433%	$54.4127	$54.41	$54.40	$54.40
Purchase #7	$85.56	4.239%	$89.1869	$89.19	$89.20	$89.20
7 purchase totals =	$786.38		$858.2185	$858.23	$858.25	$858.10