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	$83.82	9.602%	$91.8684	$91.87	$91.85	$91.90
Purchase #2	$39.62	6.360%	$42.1398	$42.14	$42.15	$42.10
Purchase #3	$53.99	5.159%	$56.7753	$56.78	$56.80	$56.80
Purchase #4	$97.77	9.415%	$106.975	$106.98	$107.00	$107.00
Purchase #5	$75.65	9.169%	$82.5863	$82.59	$82.60	$82.60
Purchase #6	$92.40	4.399%	$96.4647	$96.46	$96.45	$96.50
Purchase #7	$105.35	3.291%	$108.8171	$108.82	$108.80	$108.80
7 purchase totals =	$548.60		$585.6266	$585.64	$585.65	$585.70