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	$36.42	7.464%	$39.1384	$39.14	$39.15	$39.10
Purchase #2	$44.46	8.708%	$48.3316	$48.33	$48.35	$48.30
Purchase #3	$75.88	3.328%	$78.4053	$78.41	$78.40	$78.40
Purchase #4	$131.46	9.670%	$144.1722	$144.17	$144.15	$144.20
Purchase #5	$241.50	5.766%	$255.4249	$255.42	$255.40	$255.40
Purchase #6	$210.55	11.184%	$234.0979	$234.10	$234.10	$234.10
Purchase #7	$42.71	9.651%	$46.8319	$46.83	$46.85	$46.80
7 purchase totals =	$782.98		$846.4022	$846.40	$846.40	$846.30