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	$136.49	4.335%	$142.4068	$142.41	$142.40	$142.40
Purchase #2	$87.96	7.561%	$94.6107	$94.61	$94.60	$94.60
Purchase #3	$178.79	12.234%	$200.6632	$200.66	$200.65	$200.70
Purchase #4	$113.62	3.642%	$117.758	$117.76	$117.75	$117.80
Purchase #5	$136.59	12.663%	$153.8864	$153.89	$153.90	$153.90
Purchase #6	$230.28	8.170%	$249.0939	$249.09	$249.10	$249.10
Purchase #7	$214.90	5.850%	$227.4717	$227.47	$227.45	$227.50
7 purchase totals =	$1,098.63		$1,185.8907	$1,185.89	$1,185.85	$1,186.00