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	$93.83	8.168%	$101.494	$101.49	$101.50	$101.50
Purchase #2	$245.38	12.521%	$276.104	$276.10	$276.10	$276.10
Purchase #3	$11.55	12.469%	$12.9902	$12.99	$13.00	$13.00
Purchase #4	$123.40	11.468%	$137.5515	$137.55	$137.55	$137.60
Purchase #5	$70.28	10.273%	$77.4999	$77.50	$77.50	$77.50
Purchase #6	$174.52	3.447%	$180.5357	$180.54	$180.55	$180.50
Purchase #7	$100.46	13.781%	$114.3044	$114.30	$114.30	$114.30
7 purchase totals =	$819.42		$900.4797	$900.47	$900.50	$900.50