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	$156.83	7.522%	$168.6268	$168.63	$168.65	$168.60
Purchase #2	$128.92	5.508%	$136.0209	$136.02	$136.00	$136.00
Purchase #3	$122.35	3.469%	$126.5943	$126.59	$126.60	$126.60
Purchase #4	$42.32	11.383%	$47.1373	$47.14	$47.15	$47.10
Purchase #5	$66.71	7.465%	$71.6899	$71.69	$71.70	$71.70
Purchase #6	$166.31	9.182%	$181.5806	$181.58	$181.60	$181.60
Purchase #7	$99.61	13.259%	$112.8173	$112.82	$112.80	$112.80
7 purchase totals =	$783.05		$844.4671	$844.47	$844.50	$844.40