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	$155.81	5.550%	$164.4575	$164.46	$164.45	$164.50
Purchase #2	$215.80	4.858%	$226.2836	$226.28	$226.30	$226.30
Purchase #3	$28.52	8.866%	$31.0486	$31.05	$31.05	$31.00
Purchase #4	$149.30	10.451%	$164.9033	$164.90	$164.90	$164.90
Purchase #5	$204.52	5.358%	$215.4782	$215.48	$215.50	$215.50
Purchase #6	$29.77	10.171%	$32.7979	$32.80	$32.80	$32.80
Purchase #7	$136.71	7.443%	$146.8853	$146.89	$146.90	$146.90
7 purchase totals =	$920.43		$981.8544	$981.86	$981.90	$981.90