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	$189.28	5.832%	$200.3188	$200.32	$200.30	$200.30
Purchase #2	$200.46	10.810%	$222.1297	$222.13	$222.15	$222.10
Purchase #3	$224.97	4.437%	$234.9519	$234.95	$234.95	$235.00
Purchase #4	$151.29	10.553%	$167.2556	$167.26	$167.25	$167.30
Purchase #5	$212.46	12.169%	$238.3143	$238.31	$238.30	$238.30
Purchase #6	$47.65	6.333%	$50.6677	$50.67	$50.65	$50.70
Purchase #7	$13.35	12.452%	$15.0123	$15.01	$15.00	$15.00
7 purchase totals =	$1,039.46		$1,128.6503	$1,128.65	$1,128.60	$1,128.70