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	$40.62	6.653%	$43.3224	$43.32	$43.30	$43.30
Purchase #2	$104.70	13.132%	$118.4492	$118.45	$118.45	$118.40
Purchase #3	$164.25	6.702%	$175.258	$175.26	$175.25	$175.30
Purchase #4	$5.47	10.258%	$6.0311	$6.03	$6.05	$6.00
Purchase #5	$93.69	12.754%	$105.6392	$105.64	$105.65	$105.60
Purchase #6	$20.31	6.435%	$21.6169	$21.62	$21.60	$21.60
Purchase #7	$36.55	6.361%	$38.8749	$38.87	$38.85	$38.90
7 purchase totals =	$465.59		$509.1917	$509.19	$509.15	$509.10