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	$194.51	4.783%	$203.8134	$203.81	$203.80	$203.80
Purchase #2	$132.35	10.565%	$146.3328	$146.33	$146.35	$146.30
Purchase #3	$51.85	6.163%	$55.0455	$55.05	$55.05	$55.00
Purchase #4	$80.75	5.843%	$85.4682	$85.47	$85.45	$85.50
Purchase #5	$78.27	9.272%	$85.5272	$85.53	$85.55	$85.50
Purchase #6	$195.38	8.418%	$211.8271	$211.83	$211.85	$211.80
Purchase #7	$186.54	3.333%	$192.7574	$192.76	$192.75	$192.80
7 purchase totals =	$919.65		$980.7716	$980.78	$980.80	$980.70