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	$74.38	8.667%	$80.8265	$80.83	$80.85	$80.80
Purchase #2	$17.98	11.547%	$20.0562	$20.06	$20.05	$20.10
Purchase #3	$173.64	4.428%	$181.3288	$181.33	$181.35	$181.30
Purchase #4	$168.82	11.251%	$187.8139	$187.81	$187.80	$187.80
Purchase #5	$194.50	4.443%	$203.1416	$203.14	$203.15	$203.10
Purchase #6	$77.93	9.509%	$85.3404	$85.34	$85.35	$85.30
Purchase #7	$242.27	5.417%	$255.3938	$255.39	$255.40	$255.40
7 purchase totals =	$949.52		$1,013.9012	$1,013.90	$1,013.95	$1,013.80