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	$141.34	13.523%	$160.4534	$160.45	$160.45	$160.50
Purchase #2	$110.45	9.836%	$121.3139	$121.31	$121.30	$121.30
Purchase #3	$148.58	13.636%	$168.8404	$168.84	$168.85	$168.80
Purchase #4	$25.67	11.229%	$28.5525	$28.55	$28.55	$28.60
Purchase #5	$171.62	12.415%	$192.9266	$192.93	$192.95	$192.90
Purchase #6	$82.64	7.726%	$89.0248	$89.02	$89.00	$89.00
Purchase #7	$181.34	5.212%	$190.7914	$190.79	$190.80	$190.80
7 purchase totals =	$861.64		$951.9030	$951.89	$951.90	$951.90