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	$33.84	4.728%	$35.44	$35.44	$35.45	$35.40
Purchase #2	$40.58	6.777%	$43.3301	$43.33	$43.35	$43.30
Purchase #3	$41.72	7.283%	$44.7585	$44.76	$44.75	$44.80
Purchase #4	$58.70	13.419%	$66.577	$66.58	$66.60	$66.60
Purchase #5	$54.52	9.785%	$59.8548	$59.85	$59.85	$59.90
Purchase #6	$55.55	4.102%	$57.8287	$57.83	$57.85	$57.80
Purchase #7	$222.85	4.757%	$233.451	$233.45	$233.45	$233.50
7 purchase totals =	$507.76		$541.2401	$541.24	$541.30	$541.30