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	$210.91	5.367%	$222.2295	$222.23	$222.25	$222.20
Purchase #2	$249.49	11.762%	$278.835	$278.84	$278.85	$278.80
Purchase #3	$38.92	8.577%	$42.2582	$42.26	$42.25	$42.30
Purchase #4	$52.71	5.565%	$55.6433	$55.64	$55.65	$55.60
Purchase #5	$230.40	13.553%	$261.6261	$261.63	$261.65	$261.60
Purchase #6	$7.32	5.323%	$7.7096	$7.71	$7.70	$7.70
Purchase #7	$58.69	11.165%	$65.2427	$65.24	$65.25	$65.20
7 purchase totals =	$848.44		$933.5444	$933.55	$933.60	$933.40