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	$16.84	3.243%	$17.3861	$17.39	$17.40	$17.40
Purchase #2	$88.50	9.556%	$96.9571	$96.96	$96.95	$97.00
Purchase #3	$9.43	8.512%	$10.2327	$10.23	$10.25	$10.20
Purchase #4	$125.50	11.152%	$139.4958	$139.50	$139.50	$139.50
Purchase #5	$156.60	9.450%	$171.3987	$171.40	$171.40	$171.40
Purchase #6	$172.51	5.847%	$182.5967	$182.60	$182.60	$182.60
Purchase #7	$64.90	11.551%	$72.3966	$72.40	$72.40	$72.40
7 purchase totals =	$634.28		$690.4637	$690.48	$690.50	$690.50