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	$102.49	13.646%	$116.4758	$116.48	$116.50	$116.50
Purchase #2	$110.44	11.209%	$122.8192	$122.82	$122.80	$122.80
Purchase #3	$81.43	10.501%	$89.981	$89.98	$90.00	$90.00
Purchase #4	$159.32	3.728%	$165.2594	$165.26	$165.25	$165.30
Purchase #5	$21.34	3.297%	$22.0436	$22.04	$22.05	$22.00
Purchase #6	$143.94	8.789%	$156.5909	$156.59	$156.60	$156.60
Purchase #7	$205.48	4.286%	$214.2869	$214.29	$214.30	$214.30
7 purchase totals =	$824.44		$887.4568	$887.46	$887.50	$887.50