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	$131.42	7.261%	$140.9624	$140.96	$140.95	$141.00
Purchase #2	$240.62	12.243%	$270.0791	$270.08	$270.10	$270.10
Purchase #3	$146.65	3.190%	$151.3281	$151.33	$151.35	$151.30
Purchase #4	$250.56	11.326%	$278.9384	$278.94	$278.95	$278.90
Purchase #5	$102.42	11.438%	$114.1348	$114.13	$114.15	$114.10
Purchase #6	$19.43	11.262%	$21.6182	$21.62	$21.60	$21.60
Purchase #7	$51.26	5.782%	$54.2239	$54.22	$54.20	$54.20
7 purchase totals =	$942.36		$1,031.2849	$1,031.28	$1,031.30	$1,031.20