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	$242.28	12.103%	$271.6031	$271.60	$271.60	$271.60
Purchase #2	$170.77	5.861%	$180.7788	$180.78	$180.80	$180.80
Purchase #3	$88.76	12.513%	$99.8665	$99.87	$99.85	$99.90
Purchase #4	$206.97	12.790%	$233.4415	$233.44	$233.45	$233.40
Purchase #5	$171.98	13.168%	$194.6263	$194.63	$194.65	$194.60
Purchase #6	$229.53	12.281%	$257.7186	$257.72	$257.70	$257.70
Purchase #7	$112.60	13.366%	$127.6501	$127.65	$127.65	$127.70
7 purchase totals =	$1,222.89		$1,365.6849	$1,365.69	$1,365.70	$1,365.70