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	$158.60	12.567%	$178.5313	$178.53	$178.55	$178.50
Purchase #2	$40.81	7.541%	$43.8875	$43.89	$43.90	$43.90
Purchase #3	$134.82	6.559%	$143.6628	$143.66	$143.65	$143.70
Purchase #4	$206.93	11.553%	$230.8366	$230.84	$230.85	$230.80
Purchase #5	$226.37	3.403%	$234.0734	$234.07	$234.05	$234.10
Purchase #6	$77.50	6.173%	$82.2841	$82.28	$82.30	$82.30
Purchase #7	$152.37	11.383%	$169.7143	$169.71	$169.70	$169.70
7 purchase totals =	$997.40		$1,082.9900	$1,082.98	$1,083.00	$1,083.00