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	$54.66	7.537%	$58.7797	$58.78	$58.80	$58.80
Purchase #2	$245.98	3.790%	$255.3026	$255.30	$255.30	$255.30
Purchase #3	$138.50	10.130%	$152.5301	$152.53	$152.55	$152.50
Purchase #4	$58.68	13.386%	$66.5349	$66.53	$66.55	$66.50
Purchase #5	$158.54	7.808%	$170.9188	$170.92	$170.90	$170.90
Purchase #6	$11.30	8.254%	$12.2327	$12.23	$12.25	$12.20
Purchase #7	$56.58	4.853%	$59.3258	$59.33	$59.35	$59.30
7 purchase totals =	$724.24		$775.6246	$775.62	$775.70	$775.50