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	$240.94	8.257%	$260.8344	$260.83	$260.85	$260.80
Purchase #2	$129.77	13.188%	$146.8841	$146.88	$146.90	$146.90
Purchase #3	$155.66	5.718%	$164.5606	$164.56	$164.55	$164.60
Purchase #4	$74.31	12.477%	$83.5817	$83.58	$83.60	$83.60
Purchase #5	$245.88	12.551%	$276.7404	$276.74	$276.75	$276.70
Purchase #6	$61.32	13.798%	$69.7809	$69.78	$69.80	$69.80
Purchase #7	$78.87	5.401%	$83.1298	$83.13	$83.15	$83.10
7 purchase totals =	$986.75		$1,085.5119	$1,085.50	$1,085.60	$1,085.50