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	$30.52	13.325%	$34.5868	$34.59	$34.60	$34.60
Purchase #2	$97.88	7.439%	$105.1613	$105.16	$105.15	$105.20
Purchase #3	$88.27	9.242%	$96.4279	$96.43	$96.45	$96.40
Purchase #4	$95.45	6.854%	$101.9921	$101.99	$102.00	$102.00
Purchase #5	$31.56	12.461%	$35.4927	$35.49	$35.50	$35.50
Purchase #6	$188.83	13.603%	$214.5165	$214.52	$214.50	$214.50
Purchase #7	$52.93	12.500%	$59.5463	$59.55	$59.55	$59.50
7 purchase totals =	$585.44		$647.7236	$647.73	$647.75	$647.70