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	$18.92	10.373%	$20.8826	$20.88	$20.90	$20.90
Purchase #2	$127.77	9.508%	$139.9184	$139.92	$139.90	$139.90
Purchase #3	$45.25	13.735%	$51.4651	$51.47	$51.45	$51.50
Purchase #4	$109.47	10.135%	$120.5648	$120.56	$120.55	$120.60
Purchase #5	$94.69	8.194%	$102.4489	$102.45	$102.45	$102.40
Purchase #6	$125.96	9.436%	$137.8456	$137.85	$137.85	$137.80
Purchase #7	$55.87	7.417%	$60.0139	$60.01	$60.00	$60.00
7 purchase totals =	$577.93		$633.1393	$633.14	$633.10	$633.10