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	$96.42	5.238%	$101.4705	$101.47	$101.45	$101.50
Purchase #2	$122.80	8.381%	$133.0919	$133.09	$133.10	$133.10
Purchase #3	$58.27	6.482%	$62.0471	$62.05	$62.05	$62.00
Purchase #4	$136.66	7.482%	$146.8849	$146.88	$146.90	$146.90
Purchase #5	$54.85	8.562%	$59.5463	$59.55	$59.55	$59.50
Purchase #6	$104.37	9.224%	$113.9971	$114.00	$114.00	$114.00
Purchase #7	$46.35	4.622%	$48.4923	$48.49	$48.50	$48.50
7 purchase totals =	$619.72		$665.5301	$665.53	$665.55	$665.50