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	$223.87	11.821%	$250.3337	$250.33	$250.35	$250.30
Purchase #2	$195.32	10.443%	$215.7173	$215.72	$215.70	$215.70
Purchase #3	$109.69	13.795%	$124.8217	$124.82	$124.80	$124.80
Purchase #4	$133.94	6.636%	$142.8283	$142.83	$142.85	$142.80
Purchase #5	$197.65	6.513%	$210.5229	$210.52	$210.50	$210.50
Purchase #6	$123.76	3.415%	$127.9864	$127.99	$128.00	$128.00
Purchase #7	$85.75	11.124%	$95.2888	$95.29	$95.30	$95.30
7 purchase totals =	$1,069.98		$1,167.4991	$1,167.50	$1,167.50	$1,167.40