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	$105.59	13.324%	$119.6588	$119.66	$119.65	$119.70
Purchase #2	$163.75	6.836%	$174.944	$174.94	$174.95	$174.90
Purchase #3	$90.88	10.508%	$100.4297	$100.43	$100.45	$100.40
Purchase #4	$74.74	6.836%	$79.8492	$79.85	$79.85	$79.80
Purchase #5	$75.78	4.432%	$79.1386	$79.14	$79.15	$79.10
Purchase #6	$240.59	6.166%	$255.4248	$255.42	$255.40	$255.40
Purchase #7	$49.73	13.298%	$56.3431	$56.34	$56.35	$56.30
7 purchase totals =	$801.06		$865.7882	$865.78	$865.80	$865.60