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	$52.50	3.853%	$54.5228	$54.52	$54.50	$54.50
Purchase #2	$200.68	6.435%	$213.5938	$213.59	$213.60	$213.60
Purchase #3	$210.68	11.767%	$235.4707	$235.47	$235.45	$235.50
Purchase #4	$237.93	12.146%	$266.829	$266.83	$266.85	$266.80
Purchase #5	$172.89	4.392%	$180.4833	$180.48	$180.50	$180.50
Purchase #6	$76.27	12.521%	$85.8198	$85.82	$85.80	$85.80
Purchase #7	$165.69	4.564%	$173.2521	$173.25	$173.25	$173.30
7 purchase totals =	$1,116.64		$1,209.9715	$1,209.96	$1,209.95	$1,210.00