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	$6.81	12.599%	$7.668	$7.67	$7.65	$7.70
Purchase #2	$81.55	9.189%	$89.0436	$89.04	$89.05	$89.00
Purchase #3	$241.69	3.786%	$250.8404	$250.84	$250.85	$250.80
Purchase #4	$86.76	4.227%	$90.4273	$90.43	$90.45	$90.40
Purchase #5	$206.82	6.789%	$220.861	$220.86	$220.85	$220.90
Purchase #6	$174.72	12.275%	$196.1669	$196.17	$196.15	$196.20
Purchase #7	$105.30	8.435%	$114.1821	$114.18	$114.20	$114.20
7 purchase totals =	$903.65		$969.1893	$969.19	$969.20	$969.20