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	$77.65	3.661%	$80.4928	$80.49	$80.50	$80.50
Purchase #2	$154.98	4.131%	$161.3822	$161.38	$161.40	$161.40
Purchase #3	$51.89	3.510%	$53.7113	$53.71	$53.70	$53.70
Purchase #4	$17.62	9.258%	$19.2513	$19.25	$19.25	$19.30
Purchase #5	$229.77	9.629%	$251.8946	$251.89	$251.90	$251.90
Purchase #6	$173.52	13.445%	$196.8498	$196.85	$196.85	$196.80
Purchase #7	$6.29	5.681%	$6.6473	$6.65	$6.65	$6.60
7 purchase totals =	$711.72		$770.2293	$770.22	$770.25	$770.20