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	$102.44	5.152%	$107.7177	$107.72	$107.70	$107.70
Purchase #2	$188.59	5.674%	$199.2906	$199.29	$199.30	$199.30
Purchase #3	$132.84	10.328%	$146.5597	$146.56	$146.55	$146.60
Purchase #4	$7.84	7.163%	$8.4016	$8.40	$8.40	$8.40
Purchase #5	$53.43	11.238%	$59.4345	$59.43	$59.45	$59.40
Purchase #6	$103.56	7.576%	$111.4057	$111.41	$111.40	$111.40
Purchase #7	$48.37	11.759%	$54.0578	$54.06	$54.05	$54.10
7 purchase totals =	$637.07		$686.8676	$686.87	$686.85	$686.90