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	$120.64	3.432%	$124.7804	$124.78	$124.80	$124.80
Purchase #2	$171.76	5.225%	$180.7345	$180.73	$180.75	$180.70
Purchase #3	$49.59	13.237%	$56.1542	$56.15	$56.15	$56.20
Purchase #4	$105.50	5.546%	$111.351	$111.35	$111.35	$111.40
Purchase #5	$41.99	3.314%	$43.3815	$43.38	$43.40	$43.40
Purchase #6	$208.72	4.848%	$218.8387	$218.84	$218.85	$218.80
Purchase #7	$77.58	7.619%	$83.4908	$83.49	$83.50	$83.50
7 purchase totals =	$775.78		$818.7311	$818.72	$818.80	$818.80