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	$108.56	5.342%	$114.3593	$114.36	$114.35	$114.40
Purchase #2	$119.69	6.744%	$127.7619	$127.76	$127.75	$127.80
Purchase #3	$156.58	13.479%	$177.6854	$177.69	$177.70	$177.70
Purchase #4	$121.86	8.212%	$131.8671	$131.87	$131.85	$131.90
Purchase #5	$79.66	13.355%	$90.2986	$90.30	$90.30	$90.30
Purchase #6	$50.69	8.247%	$54.8704	$54.87	$54.85	$54.90
Purchase #7	$146.74	12.436%	$164.9886	$164.99	$165.00	$165.00
7 purchase totals =	$783.78		$861.8313	$861.84	$861.80	$862.00