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	$38.64	4.115%	$40.23	$40.23	$40.25	$40.20
Purchase #2	$144.78	10.232%	$159.5939	$159.59	$159.60	$159.60
Purchase #3	$37.54	10.412%	$41.4487	$41.45	$41.45	$41.40
Purchase #4	$142.85	12.731%	$161.0362	$161.04	$161.05	$161.00
Purchase #5	$41.93	8.105%	$45.3284	$45.33	$45.35	$45.30
Purchase #6	$12.90	9.380%	$14.11	$14.11	$14.10	$14.10
Purchase #7	$171.67	12.328%	$192.8335	$192.83	$192.85	$192.80
7 purchase totals =	$590.31		$654.5807	$654.58	$654.65	$654.40