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	$55.44	3.772%	$57.5312	$57.53	$57.55	$57.50
Purchase #2	$5.29	4.396%	$5.5225	$5.52	$5.50	$5.50
Purchase #3	$211.77	5.509%	$223.4364	$223.44	$223.45	$223.40
Purchase #4	$153.99	12.172%	$172.7337	$172.73	$172.75	$172.70
Purchase #5	$143.68	3.215%	$148.2993	$148.30	$148.30	$148.30
Purchase #6	$16.54	11.557%	$18.4515	$18.45	$18.45	$18.50
Purchase #7	$27.94	3.407%	$28.8919	$28.89	$28.90	$28.90
7 purchase totals =	$614.65		$654.8665	$654.86	$654.90	$654.80