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	$214.54	10.654%	$237.3971	$237.40	$237.40	$237.40
Purchase #2	$211.63	5.735%	$223.767	$223.77	$223.75	$223.80
Purchase #3	$40.89	5.367%	$43.0846	$43.08	$43.10	$43.10
Purchase #4	$210.78	8.460%	$228.612	$228.61	$228.60	$228.60
Purchase #5	$79.59	4.205%	$82.9368	$82.94	$82.95	$82.90
Purchase #6	$125.92	13.820%	$143.3221	$143.32	$143.30	$143.30
Purchase #7	$42.94	3.669%	$44.5155	$44.52	$44.50	$44.50
7 purchase totals =	$926.29		$1,003.6351	$1,003.64	$1,003.60	$1,003.60