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	$161.96	10.241%	$178.5463	$178.55	$178.55	$178.50
Purchase #2	$135.86	11.551%	$151.5532	$151.55	$151.55	$151.60
Purchase #3	$10.25	7.629%	$11.032	$11.03	$11.05	$11.00
Purchase #4	$124.53	3.178%	$128.4876	$128.49	$128.50	$128.50
Purchase #5	$96.63	13.671%	$109.8403	$109.84	$109.85	$109.80
Purchase #6	$223.81	10.491%	$247.2899	$247.29	$247.30	$247.30
Purchase #7	$97.91	5.435%	$103.2314	$103.23	$103.25	$103.20
7 purchase totals =	$850.95		$929.9807	$929.98	$930.05	$929.90