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	$25.73	10.669%	$28.4751	$28.48	$28.50	$28.50
Purchase #2	$165.70	4.338%	$172.8881	$172.89	$172.90	$172.90
Purchase #3	$231.81	10.675%	$256.5557	$256.56	$256.55	$256.60
Purchase #4	$27.88	10.830%	$30.8994	$30.90	$30.90	$30.90
Purchase #5	$37.71	11.786%	$42.1545	$42.15	$42.15	$42.20
Purchase #6	$193.66	12.453%	$217.7765	$217.78	$217.80	$217.80
Purchase #7	$152.27	9.458%	$166.6717	$166.67	$166.65	$166.70
7 purchase totals =	$834.76		$915.4210	$915.43	$915.45	$915.60