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	$217.27	3.137%	$224.0858	$224.09	$224.10	$224.10
Purchase #2	$219.73	12.374%	$246.9194	$246.92	$246.90	$246.90
Purchase #3	$86.28	6.622%	$91.9935	$91.99	$92.00	$92.00
Purchase #4	$135.65	4.626%	$141.9252	$141.93	$141.95	$141.90
Purchase #5	$37.93	12.290%	$42.5916	$42.59	$42.60	$42.60
Purchase #6	$166.54	3.719%	$172.7336	$172.73	$172.75	$172.70
Purchase #7	$52.83	10.107%	$58.1695	$58.17	$58.15	$58.20
7 purchase totals =	$916.23		$978.4186	$978.42	$978.45	$978.40