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	$48.64	12.315%	$54.63	$54.63	$54.65	$54.60
Purchase #2	$52.63	7.367%	$56.5073	$56.51	$56.50	$56.50
Purchase #3	$33.48	4.110%	$34.856	$34.86	$34.85	$34.90
Purchase #4	$146.75	12.281%	$164.7724	$164.77	$164.75	$164.80
Purchase #5	$81.91	10.526%	$90.5318	$90.53	$90.55	$90.50
Purchase #6	$50.33	8.617%	$54.6669	$54.67	$54.65	$54.70
Purchase #7	$125.39	13.667%	$142.5271	$142.53	$142.55	$142.50
7 purchase totals =	$539.13		$598.4915	$598.50	$598.50	$598.50