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	$122.49	9.690%	$134.3593	$134.36	$134.35	$134.40
Purchase #2	$156.43	10.601%	$173.0131	$173.01	$173.00	$173.00
Purchase #3	$42.29	10.861%	$46.8831	$46.88	$46.90	$46.90
Purchase #4	$104.88	9.274%	$114.6066	$114.61	$114.60	$114.60
Purchase #5	$31.37	7.289%	$33.6566	$33.66	$33.65	$33.70
Purchase #6	$90.64	10.398%	$100.0647	$100.06	$100.05	$100.10
Purchase #7	$31.77	12.563%	$35.7613	$35.76	$35.75	$35.80
7 purchase totals =	$579.87		$638.3447	$638.34	$638.30	$638.50