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	$79.99	12.315%	$89.8408	$89.84	$89.85	$89.80
Purchase #2	$214.53	5.533%	$226.3999	$226.40	$226.40	$226.40
Purchase #3	$216.36	7.710%	$233.0414	$233.04	$233.05	$233.00
Purchase #4	$203.69	6.820%	$217.5817	$217.58	$217.60	$217.60
Purchase #5	$203.75	13.576%	$231.4111	$231.41	$231.40	$231.40
Purchase #6	$249.72	11.458%	$278.3329	$278.33	$278.35	$278.30
Purchase #7	$145.72	4.767%	$152.6665	$152.67	$152.65	$152.70
7 purchase totals =	$1,313.76		$1,429.2743	$1,429.27	$1,429.30	$1,429.20