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	$158.80	5.844%	$168.0803	$168.08	$168.10	$168.10
Purchase #2	$168.91	12.572%	$190.1454	$190.15	$190.15	$190.10
Purchase #3	$48.74	10.232%	$53.7271	$53.73	$53.75	$53.70
Purchase #4	$240.25	5.540%	$253.5599	$253.56	$253.55	$253.60
Purchase #5	$23.69	7.813%	$25.5409	$25.54	$25.55	$25.50
Purchase #6	$81.58	13.667%	$92.7295	$92.73	$92.75	$92.70
Purchase #7	$74.34	10.726%	$82.3137	$82.31	$82.30	$82.30
7 purchase totals =	$796.31		$866.0968	$866.10	$866.15	$866.00