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	$113.77	11.373%	$126.7091	$126.71	$126.70	$126.70
Purchase #2	$106.40	4.676%	$111.3753	$111.38	$111.40	$111.40
Purchase #3	$137.75	9.744%	$151.1724	$151.17	$151.15	$151.20
Purchase #4	$90.57	4.383%	$94.5397	$94.54	$94.55	$94.50
Purchase #5	$126.61	8.794%	$137.7441	$137.74	$137.75	$137.70
Purchase #6	$115.68	7.470%	$124.3213	$124.32	$124.30	$124.30
Purchase #7	$131.52	9.535%	$144.0604	$144.06	$144.05	$144.10
7 purchase totals =	$822.30		$889.9223	$889.92	$889.90	$889.90