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	$241.68	5.662%	$255.3639	$255.36	$255.35	$255.40
Purchase #2	$184.93	10.714%	$204.7434	$204.74	$204.75	$204.70
Purchase #3	$91.67	8.844%	$99.7773	$99.78	$99.80	$99.80
Purchase #4	$200.48	4.608%	$209.7181	$209.72	$209.70	$209.70
Purchase #5	$81.71	9.640%	$89.5868	$89.59	$89.60	$89.60
Purchase #6	$33.89	13.352%	$38.415	$38.42	$38.40	$38.40
Purchase #7	$120.66	12.713%	$135.9995	$136.00	$136.00	$136.00
7 purchase totals =	$955.02		$1,033.6040	$1,033.61	$1,033.60	$1,033.60