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	$187.59	13.668%	$213.2298	$213.23	$213.25	$213.20
Purchase #2	$110.26	4.710%	$115.4532	$115.45	$115.45	$115.50
Purchase #3	$60.63	5.797%	$64.1447	$64.14	$64.15	$64.10
Purchase #4	$47.92	7.797%	$51.6563	$51.66	$51.65	$51.70
Purchase #5	$98.89	6.247%	$105.0677	$105.07	$105.05	$105.10
Purchase #6	$41.89	4.808%	$43.9041	$43.90	$43.90	$43.90
Purchase #7	$41.76	10.544%	$46.1632	$46.16	$46.15	$46.20
7 purchase totals =	$588.94		$639.6190	$639.61	$639.60	$639.70