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	$79.89	13.556%	$90.7199	$90.72	$90.70	$90.70
Purchase #2	$140.29	7.107%	$150.2604	$150.26	$150.25	$150.30
Purchase #3	$131.92	10.357%	$145.583	$145.58	$145.60	$145.60
Purchase #4	$181.98	6.874%	$194.4893	$194.49	$194.50	$194.50
Purchase #5	$6.27	7.211%	$6.7221	$6.72	$6.70	$6.70
Purchase #6	$28.50	4.313%	$29.7292	$29.73	$29.75	$29.70
Purchase #7	$96.29	9.707%	$105.6369	$105.64	$105.65	$105.60
7 purchase totals =	$665.14		$723.1408	$723.14	$723.15	$723.10