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	$177.45	5.223%	$186.7182	$186.72	$186.70	$186.70
Purchase #2	$167.37	7.764%	$180.3646	$180.36	$180.35	$180.40
Purchase #3	$200.52	10.810%	$222.1962	$222.20	$222.20	$222.20
Purchase #4	$120.72	5.240%	$127.0457	$127.05	$127.05	$127.00
Purchase #5	$13.68	10.798%	$15.1572	$15.16	$15.15	$15.20
Purchase #6	$53.83	10.597%	$59.5344	$59.53	$59.55	$59.50
Purchase #7	$170.32	5.164%	$179.1153	$179.12	$179.10	$179.10
7 purchase totals =	$903.89		$970.1316	$970.14	$970.10	$970.10