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	$78.51	12.712%	$88.4902	$88.49	$88.50	$88.50
Purchase #2	$147.79	5.231%	$155.5209	$155.52	$155.50	$155.50
Purchase #3	$17.32	10.220%	$19.0901	$19.09	$19.10	$19.10
Purchase #4	$214.41	9.390%	$234.5431	$234.54	$234.55	$234.50
Purchase #5	$174.59	10.529%	$192.9726	$192.97	$192.95	$193.00
Purchase #6	$103.77	6.536%	$110.5524	$110.55	$110.55	$110.60
Purchase #7	$83.46	7.385%	$89.6235	$89.62	$89.60	$89.60
7 purchase totals =	$819.85		$890.7928	$890.78	$890.75	$890.80