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	$17.25	6.179%	$18.3159	$18.32	$18.30	$18.30
Purchase #2	$235.52	13.548%	$267.4282	$267.43	$267.45	$267.40
Purchase #3	$83.71	10.793%	$92.7448	$92.74	$92.75	$92.70
Purchase #4	$38.80	11.585%	$43.295	$43.30	$43.30	$43.30
Purchase #5	$120.83	9.130%	$131.8618	$131.86	$131.85	$131.90
Purchase #6	$73.48	10.482%	$81.1822	$81.18	$81.20	$81.20
Purchase #7	$35.79	10.582%	$39.5773	$39.58	$39.60	$39.60
7 purchase totals =	$605.38		$674.4052	$674.41	$674.45	$674.40