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	$108.35	7.338%	$116.3007	$116.30	$116.30	$116.30
Purchase #2	$114.99	12.169%	$128.9831	$128.98	$129.00	$129.00
Purchase #3	$162.38	6.821%	$173.4559	$173.46	$173.45	$173.50
Purchase #4	$118.81	10.371%	$131.1318	$131.13	$131.15	$131.10
Purchase #5	$147.80	13.786%	$168.1757	$168.18	$168.20	$168.20
Purchase #6	$212.90	4.144%	$221.7226	$221.72	$221.70	$221.70
Purchase #7	$178.80	7.237%	$191.7398	$191.74	$191.75	$191.70
7 purchase totals =	$1,044.03		$1,131.5096	$1,131.51	$1,131.55	$1,131.50