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	$111.26	6.382%	$118.3606	$118.36	$118.35	$118.40
Purchase #2	$106.45	5.860%	$112.688	$112.69	$112.70	$112.70
Purchase #3	$95.29	5.696%	$100.7177	$100.72	$100.70	$100.70
Purchase #4	$114.85	10.682%	$127.1183	$127.12	$127.10	$127.10
Purchase #5	$160.69	13.406%	$182.2321	$182.23	$182.25	$182.20
Purchase #6	$100.50	12.492%	$113.0545	$113.05	$113.05	$113.10
Purchase #7	$71.29	7.428%	$76.5854	$76.59	$76.60	$76.60
7 purchase totals =	$760.33		$830.7566	$830.76	$830.75	$830.80