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	$137.64	6.515%	$146.6072	$146.61	$146.60	$146.60
Purchase #2	$184.77	3.187%	$190.6586	$190.66	$190.65	$190.70
Purchase #3	$90.79	10.496%	$100.3193	$100.32	$100.30	$100.30
Purchase #4	$156.86	10.240%	$172.9225	$172.92	$172.90	$172.90
Purchase #5	$87.87	5.661%	$92.8443	$92.84	$92.85	$92.80
Purchase #6	$123.56	3.385%	$127.7425	$127.74	$127.75	$127.70
Purchase #7	$17.46	4.330%	$18.216	$18.22	$18.20	$18.20
7 purchase totals =	$798.95		$849.3104	$849.31	$849.25	$849.20