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	$179.90	13.832%	$204.7838	$204.78	$204.80	$204.80
Purchase #2	$73.36	12.599%	$82.6026	$82.60	$82.60	$82.60
Purchase #3	$41.77	9.859%	$45.8881	$45.89	$45.90	$45.90
Purchase #4	$168.37	5.814%	$178.159	$178.16	$178.15	$178.20
Purchase #5	$26.32	5.435%	$27.7505	$27.75	$27.75	$27.80
Purchase #6	$43.61	4.874%	$45.7356	$45.74	$45.75	$45.70
Purchase #7	$69.55	10.205%	$76.6476	$76.65	$76.65	$76.60
7 purchase totals =	$602.88		$661.5672	$661.57	$661.60	$661.60