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	$157.27	5.590%	$166.0614	$166.06	$166.05	$166.10
Purchase #2	$89.72	8.352%	$97.2134	$97.21	$97.20	$97.20
Purchase #3	$164.63	8.619%	$178.8195	$178.82	$178.80	$178.80
Purchase #4	$126.97	10.659%	$140.5037	$140.50	$140.50	$140.50
Purchase #5	$226.78	10.168%	$249.839	$249.84	$249.85	$249.80
Purchase #6	$88.31	13.276%	$100.034	$100.03	$100.05	$100.00
Purchase #7	$132.71	6.592%	$141.4582	$141.46	$141.45	$141.50
7 purchase totals =	$986.39		$1,073.9292	$1,073.92	$1,073.90	$1,073.90