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	$102.35	12.481%	$115.1243	$115.12	$115.10	$115.10
Purchase #2	$172.26	8.147%	$186.294	$186.29	$186.30	$186.30
Purchase #3	$137.86	9.251%	$150.6134	$150.61	$150.60	$150.60
Purchase #4	$53.39	3.826%	$55.4327	$55.43	$55.45	$55.40
Purchase #5	$69.94	4.844%	$73.3279	$73.33	$73.35	$73.30
Purchase #6	$52.42	13.574%	$59.5355	$59.54	$59.55	$59.50
Purchase #7	$142.81	10.772%	$158.1935	$158.19	$158.20	$158.20
7 purchase totals =	$731.03		$798.5213	$798.51	$798.55	$798.40