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	$139.51	12.846%	$157.4315	$157.43	$157.45	$157.40
Purchase #2	$75.69	8.805%	$82.3545	$82.35	$82.35	$82.40
Purchase #3	$130.30	10.726%	$144.276	$144.28	$144.30	$144.30
Purchase #4	$102.77	5.221%	$108.1356	$108.14	$108.15	$108.10
Purchase #5	$245.99	8.785%	$267.6002	$267.60	$267.60	$267.60
Purchase #6	$84.96	5.322%	$89.4816	$89.48	$89.50	$89.50
Purchase #7	$69.52	12.388%	$78.1321	$78.13	$78.15	$78.10
7 purchase totals =	$848.74		$927.4115	$927.41	$927.50	$927.40