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	$17.35	5.727%	$18.3436	$18.34	$18.35	$18.30
Purchase #2	$194.39	10.698%	$215.1858	$215.19	$215.20	$215.20
Purchase #3	$149.57	12.226%	$167.8564	$167.86	$167.85	$167.90
Purchase #4	$150.72	10.320%	$166.2743	$166.27	$166.25	$166.30
Purchase #5	$41.34	12.410%	$46.4703	$46.47	$46.45	$46.50
Purchase #6	$146.58	10.807%	$162.4209	$162.42	$162.40	$162.40
Purchase #7	$248.76	13.687%	$282.8078	$282.81	$282.80	$282.80
7 purchase totals =	$948.71		$1,059.3591	$1,059.36	$1,059.30	$1,059.40