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	$55.62	3.840%	$57.7558	$57.76	$57.75	$57.80
Purchase #2	$115.58	10.848%	$128.1181	$128.12	$128.10	$128.10
Purchase #3	$164.38	12.803%	$185.4256	$185.43	$185.45	$185.40
Purchase #4	$39.27	3.392%	$40.602	$40.60	$40.60	$40.60
Purchase #5	$38.78	9.612%	$42.5075	$42.51	$42.50	$42.50
Purchase #6	$127.38	11.279%	$141.7472	$141.75	$141.75	$141.70
Purchase #7	$21.28	3.516%	$22.0282	$22.03	$22.05	$22.00
7 purchase totals =	$562.29		$618.1844	$618.20	$618.20	$618.10