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	$13.69	10.821%	$15.1714	$15.17	$15.15	$15.20
Purchase #2	$49.95	4.866%	$52.3806	$52.38	$52.40	$52.40
Purchase #3	$188.35	4.346%	$196.5357	$196.54	$196.55	$196.50
Purchase #4	$156.26	13.342%	$177.1082	$177.11	$177.10	$177.10
Purchase #5	$72.43	12.670%	$81.6069	$81.61	$81.60	$81.60
Purchase #6	$141.69	4.779%	$148.4614	$148.46	$148.45	$148.50
Purchase #7	$118.35	7.424%	$127.1363	$127.14	$127.15	$127.10
7 purchase totals =	$740.72		$798.4005	$798.41	$798.40	$798.40