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	$38.32	3.623%	$39.7083	$39.71	$39.70	$39.70
Purchase #2	$106.44	7.615%	$114.5454	$114.55	$114.55	$114.50
Purchase #3	$146.31	11.344%	$162.9074	$162.91	$162.90	$162.90
Purchase #4	$53.92	6.194%	$57.2598	$57.26	$57.25	$57.30
Purchase #5	$112.79	9.651%	$123.6754	$123.68	$123.70	$123.70
Purchase #6	$142.88	10.771%	$158.2696	$158.27	$158.25	$158.30
Purchase #7	$18.28	3.175%	$18.8604	$18.86	$18.85	$18.90
7 purchase totals =	$618.94		$675.2263	$675.24	$675.20	$675.30