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	$110.77	11.245%	$123.2261	$123.23	$123.25	$123.20
Purchase #2	$38.54	8.284%	$41.7327	$41.73	$41.75	$41.70
Purchase #3	$32.77	13.602%	$37.2274	$37.23	$37.25	$37.20
Purchase #4	$48.90	8.598%	$53.1044	$53.10	$53.10	$53.10
Purchase #5	$117.84	12.561%	$132.6419	$132.64	$132.65	$132.60
Purchase #6	$35.95	13.314%	$40.7364	$40.74	$40.75	$40.70
Purchase #7	$121.84	8.656%	$132.3865	$132.39	$132.40	$132.40
7 purchase totals =	$506.61		$561.0554	$561.06	$561.15	$560.90