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	$30.92	11.592%	$34.5042	$34.50	$34.50	$34.50
Purchase #2	$110.88	11.398%	$123.5181	$123.52	$123.50	$123.50
Purchase #3	$172.76	6.211%	$183.4901	$183.49	$183.50	$183.50
Purchase #4	$241.36	9.600%	$264.5306	$264.53	$264.55	$264.50
Purchase #5	$111.36	10.680%	$123.2532	$123.25	$123.25	$123.30
Purchase #6	$35.35	7.399%	$37.9655	$37.97	$37.95	$38.00
Purchase #7	$116.43	3.232%	$120.193	$120.19	$120.20	$120.20
7 purchase totals =	$819.06		$887.4547	$887.45	$887.45	$887.50