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	$51.61	13.716%	$58.6888	$58.69	$58.70	$58.70
Purchase #2	$28.84	9.744%	$31.6502	$31.65	$31.65	$31.70
Purchase #3	$160.98	8.169%	$174.1305	$174.13	$174.15	$174.10
Purchase #4	$153.78	12.242%	$172.6057	$172.61	$172.60	$172.60
Purchase #5	$43.53	5.725%	$46.0221	$46.02	$46.00	$46.00
Purchase #6	$86.31	4.434%	$90.137	$90.14	$90.15	$90.10
Purchase #7	$242.83	10.537%	$268.417	$268.42	$268.40	$268.40
7 purchase totals =	$767.88		$841.6513	$841.66	$841.65	$841.60