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	$80.57	11.565%	$89.8879	$89.89	$89.90	$89.90
Purchase #2	$94.89	5.816%	$100.4088	$100.41	$100.40	$100.40
Purchase #3	$32.93	9.184%	$35.9543	$35.95	$35.95	$36.00
Purchase #4	$19.41	7.764%	$20.917	$20.92	$20.90	$20.90
Purchase #5	$134.43	10.297%	$148.2723	$148.27	$148.25	$148.30
Purchase #6	$94.68	10.372%	$104.5002	$104.50	$104.50	$104.50
Purchase #7	$222.91	6.294%	$236.94	$236.94	$236.95	$236.90
7 purchase totals =	$679.82		$736.8805	$736.88	$736.85	$736.90