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	$99.87	8.583%	$108.4418	$108.44	$108.45	$108.40
Purchase #2	$150.84	7.747%	$162.5256	$162.53	$162.55	$162.50
Purchase #3	$103.34	10.751%	$114.4501	$114.45	$114.45	$114.50
Purchase #4	$163.65	13.383%	$185.5513	$185.55	$185.55	$185.60
Purchase #5	$78.72	3.344%	$81.3524	$81.35	$81.35	$81.40
Purchase #6	$147.49	12.170%	$165.4395	$165.44	$165.45	$165.40
Purchase #7	$64.51	10.146%	$71.0552	$71.06	$71.05	$71.10
7 purchase totals =	$808.42		$888.8159	$888.82	$888.85	$888.90