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	$72.60	9.596%	$79.5667	$79.57	$79.55	$79.60
Purchase #2	$55.94	11.508%	$62.3776	$62.38	$62.40	$62.40
Purchase #3	$56.27	8.463%	$61.0321	$61.03	$61.05	$61.00
Purchase #4	$181.99	5.330%	$191.6901	$191.69	$191.70	$191.70
Purchase #5	$128.86	7.429%	$138.433	$138.43	$138.45	$138.40
Purchase #6	$43.47	5.759%	$45.9734	$45.97	$45.95	$46.00
Purchase #7	$54.47	12.280%	$61.1589	$61.16	$61.15	$61.20
7 purchase totals =	$593.60		$640.2318	$640.23	$640.25	$640.30