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	$105.85	5.273%	$111.4315	$111.43	$111.45	$111.40
Purchase #2	$73.81	13.165%	$83.5271	$83.53	$83.55	$83.50
Purchase #3	$231.76	9.558%	$253.9116	$253.91	$253.90	$253.90
Purchase #4	$131.75	11.632%	$147.0752	$147.08	$147.10	$147.10
Purchase #5	$99.38	5.343%	$104.6899	$104.69	$104.70	$104.70
Purchase #6	$59.46	8.680%	$64.6211	$64.62	$64.60	$64.60
Purchase #7	$61.56	3.489%	$63.7078	$63.71	$63.70	$63.70
7 purchase totals =	$763.57		$828.9642	$828.97	$829.00	$828.90