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	$123.37	6.663%	$131.5901	$131.59	$131.60	$131.60
Purchase #2	$249.36	4.286%	$260.0476	$260.05	$260.05	$260.00
Purchase #3	$97.38	12.438%	$109.4921	$109.49	$109.50	$109.50
Purchase #4	$96.55	9.203%	$105.4355	$105.44	$105.45	$105.40
Purchase #5	$183.29	8.615%	$199.0804	$199.08	$199.10	$199.10
Purchase #6	$31.42	6.866%	$33.5773	$33.58	$33.60	$33.60
Purchase #7	$144.42	7.717%	$155.5649	$155.56	$155.55	$155.60
7 purchase totals =	$925.79		$994.7879	$994.79	$994.85	$994.80