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	$59.76	12.689%	$67.3429	$67.34	$67.35	$67.30
Purchase #2	$129.83	11.300%	$144.5008	$144.50	$144.50	$144.50
Purchase #3	$168.46	6.729%	$179.7957	$179.80	$179.80	$179.80
Purchase #4	$141.52	12.185%	$158.7642	$158.76	$158.75	$158.80
Purchase #5	$214.31	4.420%	$223.7825	$223.78	$223.80	$223.80
Purchase #6	$209.85	3.580%	$217.3626	$217.36	$217.35	$217.40
Purchase #7	$133.90	11.717%	$149.5891	$149.59	$149.60	$149.60
7 purchase totals =	$1,057.63		$1,141.1378	$1,141.13	$1,141.15	$1,141.20