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	$114.93	7.263%	$123.2774	$123.28	$123.30	$123.30
Purchase #2	$46.92	5.354%	$49.4321	$49.43	$49.45	$49.40
Purchase #3	$18.86	3.513%	$19.5226	$19.52	$19.50	$19.50
Purchase #4	$235.61	12.548%	$265.1743	$265.17	$265.15	$265.20
Purchase #5	$152.44	7.591%	$164.0117	$164.01	$164.00	$164.00
Purchase #6	$34.26	12.788%	$38.6412	$38.64	$38.65	$38.60
Purchase #7	$28.85	9.167%	$31.4947	$31.49	$31.50	$31.50
7 purchase totals =	$631.87		$691.5540	$691.54	$691.55	$691.50