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	$86.88	3.156%	$89.6219	$89.62	$89.60	$89.60
Purchase #2	$237.89	3.376%	$245.9212	$245.92	$245.90	$245.90
Purchase #3	$98.77	11.453%	$110.0821	$110.08	$110.10	$110.10
Purchase #4	$132.71	5.834%	$140.4523	$140.45	$140.45	$140.50
Purchase #5	$146.97	7.792%	$158.4219	$158.42	$158.40	$158.40
Purchase #6	$220.84	5.587%	$233.1783	$233.18	$233.20	$233.20
Purchase #7	$157.71	11.121%	$175.2489	$175.25	$175.25	$175.20
7 purchase totals =	$1,081.77		$1,152.9266	$1,152.92	$1,152.90	$1,152.90