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	$195.32	12.584%	$219.8991	$219.90	$219.90	$219.90
Purchase #2	$72.88	12.618%	$82.076	$82.08	$82.10	$82.10
Purchase #3	$210.63	13.289%	$238.6206	$238.62	$238.60	$238.60
Purchase #4	$21.53	12.111%	$24.1375	$24.14	$24.15	$24.10
Purchase #5	$128.98	7.114%	$138.1556	$138.16	$138.15	$138.20
Purchase #6	$59.97	11.507%	$66.8707	$66.87	$66.85	$66.90
Purchase #7	$166.72	3.168%	$172.0017	$172.00	$172.00	$172.00
7 purchase totals =	$856.03		$941.7612	$941.77	$941.75	$941.80