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	$89.44	12.583%	$100.6942	$100.69	$100.70	$100.70
Purchase #2	$44.91	4.345%	$46.8613	$46.86	$46.85	$46.90
Purchase #3	$28.91	8.379%	$31.3324	$31.33	$31.35	$31.30
Purchase #4	$240.33	10.662%	$265.954	$265.95	$265.95	$266.00
Purchase #5	$63.45	13.626%	$72.0957	$72.10	$72.10	$72.10
Purchase #6	$63.45	10.642%	$70.2023	$70.20	$70.20	$70.20
Purchase #7	$223.49	11.172%	$248.4583	$248.46	$248.45	$248.50
7 purchase totals =	$753.98		$835.5982	$835.59	$835.60	$835.70