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	$38.95	4.721%	$40.7888	$40.79	$40.80	$40.80
Purchase #2	$53.51	11.398%	$59.6091	$59.61	$59.60	$59.60
Purchase #3	$245.79	3.269%	$253.8249	$253.82	$253.80	$253.80
Purchase #4	$101.79	13.732%	$115.7678	$115.77	$115.75	$115.80
Purchase #5	$146.25	13.828%	$166.4735	$166.47	$166.45	$166.50
Purchase #6	$71.82	12.843%	$81.0438	$81.04	$81.05	$81.00
Purchase #7	$197.65	8.502%	$214.4542	$214.45	$214.45	$214.50
7 purchase totals =	$855.76		$931.9621	$931.95	$931.90	$932.00