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	$250.51	10.374%	$276.4979	$276.50	$276.50	$276.50
Purchase #2	$46.86	6.373%	$49.8464	$49.85	$49.85	$49.80
Purchase #3	$228.38	6.208%	$242.5578	$242.56	$242.55	$242.60
Purchase #4	$169.38	6.354%	$180.1424	$180.14	$180.15	$180.10
Purchase #5	$56.36	9.731%	$61.8444	$61.84	$61.85	$61.80
Purchase #6	$91.52	13.820%	$104.1681	$104.17	$104.15	$104.20
Purchase #7	$145.51	5.777%	$153.9161	$153.92	$153.90	$153.90
7 purchase totals =	$988.52		$1,068.9731	$1,068.98	$1,068.95	$1,068.90