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	$80.79	10.746%	$89.4717	$89.47	$89.45	$89.50
Purchase #2	$99.82	6.786%	$106.5938	$106.59	$106.60	$106.60
Purchase #3	$146.52	3.489%	$151.6321	$151.63	$151.65	$151.60
Purchase #4	$189.53	13.569%	$215.2473	$215.25	$215.25	$215.20
Purchase #5	$51.92	9.377%	$56.7885	$56.79	$56.80	$56.80
Purchase #6	$153.92	7.565%	$165.564	$165.56	$165.55	$165.60
Purchase #7	$142.69	11.224%	$158.7055	$158.71	$158.70	$158.70
7 purchase totals =	$865.19		$944.0029	$944.00	$944.00	$944.00