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	$74.95	3.782%	$77.7846	$77.78	$77.80	$77.80
Purchase #2	$52.68	7.201%	$56.4735	$56.47	$56.45	$56.50
Purchase #3	$62.38	3.455%	$64.5352	$64.54	$64.55	$64.50
Purchase #4	$54.72	3.518%	$56.645	$56.65	$56.65	$56.60
Purchase #5	$231.78	10.514%	$256.1493	$256.15	$256.15	$256.10
Purchase #6	$209.74	4.833%	$219.8767	$219.88	$219.90	$219.90
Purchase #7	$90.87	3.856%	$94.3739	$94.37	$94.35	$94.40
7 purchase totals =	$777.12		$825.8382	$825.84	$825.85	$825.80