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	$50.88	7.628%	$54.7611	$54.76	$54.75	$54.80
Purchase #2	$86.70	4.706%	$90.7801	$90.78	$90.80	$90.80
Purchase #3	$42.30	5.119%	$44.4653	$44.47	$44.45	$44.50
Purchase #4	$35.76	13.494%	$40.5855	$40.59	$40.60	$40.60
Purchase #5	$124.69	3.649%	$129.2399	$129.24	$129.25	$129.20
Purchase #6	$229.85	9.240%	$251.0881	$251.09	$251.10	$251.10
Purchase #7	$245.80	9.491%	$269.1289	$269.13	$269.15	$269.10
7 purchase totals =	$815.98		$880.0489	$880.06	$880.10	$880.10