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	$115.91	13.565%	$131.6332	$131.63	$131.65	$131.60
Purchase #2	$174.87	9.327%	$191.1801	$191.18	$191.20	$191.20
Purchase #3	$216.40	10.350%	$238.7974	$238.80	$238.80	$238.80
Purchase #4	$222.42	12.481%	$250.1802	$250.18	$250.20	$250.20
Purchase #5	$171.40	9.601%	$187.8561	$187.86	$187.85	$187.90
Purchase #6	$77.81	4.600%	$81.3893	$81.39	$81.40	$81.40
Purchase #7	$39.32	8.621%	$42.7098	$42.71	$42.70	$42.70
7 purchase totals =	$1,018.13		$1,123.7461	$1,123.75	$1,123.80	$1,123.80