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	$50.88	8.255%	$55.0801	$55.08	$55.10	$55.10
Purchase #2	$78.60	4.502%	$82.1386	$82.14	$82.15	$82.10
Purchase #3	$223.40	10.535%	$246.9352	$246.94	$246.95	$246.90
Purchase #4	$115.89	8.705%	$125.9782	$125.98	$126.00	$126.00
Purchase #5	$103.28	11.673%	$115.3359	$115.34	$115.35	$115.30
Purchase #6	$154.89	3.677%	$160.5853	$160.59	$160.60	$160.60
Purchase #7	$31.87	7.653%	$34.309	$34.31	$34.30	$34.30
7 purchase totals =	$758.81		$820.3623	$820.38	$820.45	$820.30