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	$122.82	3.680%	$127.3398	$127.34	$127.35	$127.30
Purchase #2	$126.50	8.650%	$137.4423	$137.44	$137.45	$137.40
Purchase #3	$46.73	7.706%	$50.331	$50.33	$50.35	$50.30
Purchase #4	$74.84	12.579%	$84.2541	$84.25	$84.25	$84.30
Purchase #5	$42.28	3.165%	$43.6182	$43.62	$43.60	$43.60
Purchase #6	$100.59	7.855%	$108.4913	$108.49	$108.50	$108.50
Purchase #7	$41.49	10.710%	$45.9336	$45.93	$45.95	$45.90
7 purchase totals =	$555.25		$597.4103	$597.40	$597.45	$597.30