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	$5.81	11.792%	$6.4951	$6.50	$6.50	$6.50
Purchase #2	$46.82	13.719%	$53.2432	$53.24	$53.25	$53.20
Purchase #3	$144.47	7.614%	$155.4699	$155.47	$155.45	$155.50
Purchase #4	$63.86	10.318%	$70.4491	$70.45	$70.45	$70.40
Purchase #5	$210.28	8.674%	$228.5197	$228.52	$228.50	$228.50
Purchase #6	$70.84	11.381%	$78.9023	$78.90	$78.90	$78.90
Purchase #7	$137.53	13.354%	$155.8958	$155.90	$155.90	$155.90
7 purchase totals =	$679.61		$748.9751	$748.98	$748.95	$748.90