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	$49.33	12.379%	$55.4366	$55.44	$55.45	$55.40
Purchase #2	$31.43	3.164%	$32.4244	$32.42	$32.40	$32.40
Purchase #3	$137.85	4.661%	$144.2752	$144.28	$144.30	$144.30
Purchase #4	$80.78	6.356%	$85.9144	$85.91	$85.90	$85.90
Purchase #5	$105.32	7.463%	$113.18	$113.18	$113.20	$113.20
Purchase #6	$89.52	8.159%	$96.8239	$96.82	$96.80	$96.80
Purchase #7	$185.72	7.592%	$199.8199	$199.82	$199.80	$199.80
7 purchase totals =	$679.95		$727.8744	$727.87	$727.85	$727.80