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	$238.52	11.293%	$265.4561	$265.46	$265.45	$265.50
Purchase #2	$171.56	5.334%	$180.711	$180.71	$180.70	$180.70
Purchase #3	$227.41	12.873%	$256.6845	$256.68	$256.70	$256.70
Purchase #4	$45.34	6.192%	$48.1475	$48.15	$48.15	$48.10
Purchase #5	$103.96	13.645%	$118.1453	$118.15	$118.15	$118.10
Purchase #6	$232.30	13.523%	$263.7139	$263.71	$263.70	$263.70
Purchase #7	$82.58	10.166%	$90.9751	$90.98	$91.00	$91.00
7 purchase totals =	$1,101.67		$1,223.8334	$1,223.84	$1,223.85	$1,223.80