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	$30.35	11.660%	$33.8888	$33.89	$33.90	$33.90
Purchase #2	$117.60	11.797%	$131.4733	$131.47	$131.45	$131.50
Purchase #3	$20.86	13.204%	$23.6144	$23.61	$23.60	$23.60
Purchase #4	$127.39	11.226%	$141.6908	$141.69	$141.70	$141.70
Purchase #5	$80.86	5.346%	$85.1828	$85.18	$85.20	$85.20
Purchase #6	$42.56	13.633%	$48.3622	$48.36	$48.35	$48.40
Purchase #7	$183.98	3.385%	$190.2077	$190.21	$190.20	$190.20
7 purchase totals =	$603.60		$654.4200	$654.41	$654.40	$654.50