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	$69.99	10.518%	$77.3515	$77.35	$77.35	$77.40
Purchase #2	$79.83	13.287%	$90.437	$90.44	$90.45	$90.40
Purchase #3	$93.79	7.507%	$100.8308	$100.83	$100.85	$100.80
Purchase #4	$58.92	13.820%	$67.0627	$67.06	$67.05	$67.10
Purchase #5	$130.36	6.678%	$139.0654	$139.07	$139.05	$139.10
Purchase #6	$105.85	4.857%	$110.9911	$110.99	$111.00	$111.00
Purchase #7	$141.98	10.759%	$157.2556	$157.26	$157.25	$157.30
7 purchase totals =	$680.72		$742.9941	$743.00	$743.00	$743.10