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	$42.96	13.747%	$48.8657	$48.87	$48.85	$48.90
Purchase #2	$50.31	8.842%	$54.7584	$54.76	$54.75	$54.80
Purchase #3	$167.53	6.618%	$178.6171	$178.62	$178.60	$178.60
Purchase #4	$72.63	7.320%	$77.9465	$77.95	$77.95	$77.90
Purchase #5	$86.44	11.579%	$96.4489	$96.45	$96.45	$96.40
Purchase #6	$181.96	7.807%	$196.1656	$196.17	$196.15	$196.20
Purchase #7	$139.64	4.613%	$146.0816	$146.08	$146.10	$146.10
7 purchase totals =	$741.47		$798.8838	$798.90	$798.85	$798.90