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	$92.80	8.203%	$100.4124	$100.41	$100.40	$100.40
Purchase #2	$151.49	9.170%	$165.3816	$165.38	$165.40	$165.40
Purchase #3	$29.63	13.381%	$33.5948	$33.59	$33.60	$33.60
Purchase #4	$42.28	5.207%	$44.4815	$44.48	$44.50	$44.50
Purchase #5	$152.85	4.632%	$159.93	$159.93	$159.95	$159.90
Purchase #6	$152.88	3.292%	$157.9128	$157.91	$157.90	$157.90
Purchase #7	$21.42	5.262%	$22.5471	$22.55	$22.55	$22.50
7 purchase totals =	$643.35		$684.2602	$684.25	$684.30	$684.20