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	$52.75	12.269%	$59.2219	$59.22	$59.20	$59.20
Purchase #2	$12.76	11.839%	$14.2707	$14.27	$14.25	$14.30
Purchase #3	$222.97	13.743%	$253.6128	$253.61	$253.60	$253.60
Purchase #4	$144.29	4.680%	$151.0428	$151.04	$151.05	$151.00
Purchase #5	$134.70	5.194%	$141.6963	$141.70	$141.70	$141.70
Purchase #6	$38.70	10.144%	$42.6257	$42.63	$42.65	$42.60
Purchase #7	$105.52	9.789%	$115.8494	$115.85	$115.85	$115.80
7 purchase totals =	$711.69		$778.3196	$778.32	$778.30	$778.20