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	$133.84	11.161%	$148.7779	$148.78	$148.80	$148.80
Purchase #2	$236.89	12.151%	$265.6745	$265.67	$265.65	$265.70
Purchase #3	$210.30	11.766%	$235.0439	$235.04	$235.05	$235.00
Purchase #4	$49.56	9.817%	$54.4253	$54.43	$54.45	$54.40
Purchase #5	$12.29	12.718%	$13.853	$13.85	$13.85	$13.90
Purchase #6	$28.72	10.350%	$31.6925	$31.69	$31.70	$31.70
Purchase #7	$213.83	12.520%	$240.6015	$240.60	$240.60	$240.60
7 purchase totals =	$885.43		$990.0686	$990.06	$990.10	$990.10