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	$86.87	6.314%	$92.355	$92.36	$92.35	$92.40
Purchase #2	$98.62	13.465%	$111.8992	$111.90	$111.90	$111.90
Purchase #3	$23.98	12.574%	$26.9952	$27.00	$27.00	$27.00
Purchase #4	$19.38	4.592%	$20.2699	$20.27	$20.25	$20.30
Purchase #5	$54.44	12.588%	$61.2929	$61.29	$61.30	$61.30
Purchase #6	$171.80	10.623%	$190.0503	$190.05	$190.05	$190.10
Purchase #7	$184.65	12.733%	$208.1615	$208.16	$208.15	$208.20
7 purchase totals =	$639.74		$711.0240	$711.03	$711.00	$711.20