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	$50.39	5.802%	$53.3136	$53.31	$53.30	$53.30
Purchase #2	$20.47	12.556%	$23.0402	$23.04	$23.05	$23.00
Purchase #3	$19.40	5.817%	$20.5285	$20.53	$20.55	$20.50
Purchase #4	$43.53	11.667%	$48.6086	$48.61	$48.60	$48.60
Purchase #5	$48.77	3.825%	$50.6355	$50.64	$50.65	$50.60
Purchase #6	$45.71	13.813%	$52.0239	$52.02	$52.00	$52.00
Purchase #7	$250.41	11.235%	$278.5436	$278.54	$278.55	$278.50
7 purchase totals =	$478.68		$526.6939	$526.69	$526.70	$526.50