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	$235.58	10.564%	$260.4667	$260.47	$260.45	$260.50
Purchase #2	$227.70	12.679%	$256.5701	$256.57	$256.55	$256.60
Purchase #3	$93.50	13.236%	$105.8757	$105.88	$105.90	$105.90
Purchase #4	$154.26	11.600%	$172.1542	$172.15	$172.15	$172.20
Purchase #5	$229.96	3.779%	$238.6502	$238.65	$238.65	$238.70
Purchase #6	$72.62	8.233%	$78.5988	$78.60	$78.60	$78.60
Purchase #7	$15.56	3.736%	$16.1413	$16.14	$16.15	$16.10
7 purchase totals =	$1,029.18		$1,128.4570	$1,128.46	$1,128.45	$1,128.60