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	$72.66	10.283%	$80.1316	$80.13	$80.15	$80.10
Purchase #2	$210.55	4.373%	$219.7574	$219.76	$219.75	$219.80
Purchase #3	$70.60	4.249%	$73.5998	$73.60	$73.60	$73.60
Purchase #4	$111.31	11.655%	$124.2832	$124.28	$124.30	$124.30
Purchase #5	$134.69	12.360%	$151.3377	$151.34	$151.35	$151.30
Purchase #6	$172.68	13.640%	$196.2336	$196.23	$196.25	$196.20
Purchase #7	$234.79	3.295%	$242.5263	$242.53	$242.55	$242.50
7 purchase totals =	$1,007.28		$1,087.8696	$1,087.87	$1,087.95	$1,087.80