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	$225.32	11.463%	$251.1484	$251.15	$251.15	$251.10
Purchase #2	$235.77	8.366%	$255.4945	$255.49	$255.50	$255.50
Purchase #3	$105.28	10.663%	$116.506	$116.51	$116.50	$116.50
Purchase #4	$198.80	5.392%	$209.5193	$209.52	$209.50	$209.50
Purchase #5	$44.76	10.331%	$49.3842	$49.38	$49.40	$49.40
Purchase #6	$222.33	3.424%	$229.9426	$229.94	$229.95	$229.90
Purchase #7	$73.83	5.137%	$77.6226	$77.62	$77.60	$77.60
7 purchase totals =	$1,106.09		$1,189.6176	$1,189.61	$1,189.60	$1,189.50