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	$32.33	6.261%	$34.3542	$34.35	$34.35	$34.40
Purchase #2	$143.27	7.573%	$154.1198	$154.12	$154.10	$154.10
Purchase #3	$62.37	6.773%	$66.5943	$66.59	$66.60	$66.60
Purchase #4	$99.73	4.454%	$104.172	$104.17	$104.15	$104.20
Purchase #5	$166.25	11.739%	$185.7661	$185.77	$185.75	$185.80
Purchase #6	$118.44	11.376%	$131.9137	$131.91	$131.90	$131.90
Purchase #7	$145.58	10.841%	$161.3623	$161.36	$161.35	$161.40
7 purchase totals =	$767.97		$838.2824	$838.27	$838.20	$838.40