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	$51.73	10.839%	$57.337	$57.34	$57.35	$57.30
Purchase #2	$52.95	3.412%	$54.7567	$54.76	$54.75	$54.80
Purchase #3	$222.85	12.690%	$251.1297	$251.13	$251.15	$251.10
Purchase #4	$75.45	13.292%	$85.4788	$85.48	$85.50	$85.50
Purchase #5	$112.54	4.515%	$117.6212	$117.62	$117.60	$117.60
Purchase #6	$174.32	9.480%	$190.8455	$190.85	$190.85	$190.80
Purchase #7	$61.40	6.402%	$65.3308	$65.33	$65.35	$65.30
7 purchase totals =	$751.24		$822.4997	$822.51	$822.55	$822.40