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	$34.94	7.595%	$37.5937	$37.59	$37.60	$37.60
Purchase #2	$86.68	5.443%	$91.398	$91.40	$91.40	$91.40
Purchase #3	$43.64	12.232%	$48.978	$48.98	$49.00	$49.00
Purchase #4	$170.37	5.473%	$179.6944	$179.69	$179.70	$179.70
Purchase #5	$20.63	8.460%	$22.3753	$22.38	$22.40	$22.40
Purchase #6	$103.49	13.697%	$117.665	$117.67	$117.65	$117.70
Purchase #7	$133.52	6.655%	$142.4058	$142.41	$142.40	$142.40
7 purchase totals =	$593.27		$640.1102	$640.12	$640.15	$640.20