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	$162.80	3.539%	$168.5615	$168.56	$168.55	$168.60
Purchase #2	$35.28	9.114%	$38.4954	$38.50	$38.50	$38.50
Purchase #3	$28.72	5.838%	$30.3967	$30.40	$30.40	$30.40
Purchase #4	$236.68	7.213%	$253.7517	$253.75	$253.75	$253.80
Purchase #5	$41.83	4.195%	$43.5848	$43.58	$43.60	$43.60
Purchase #6	$222.54	8.477%	$241.4047	$241.40	$241.40	$241.40
Purchase #7	$47.54	5.778%	$50.2869	$50.29	$50.30	$50.30
7 purchase totals =	$775.39		$826.4817	$826.48	$826.50	$826.60