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	$236.72	9.736%	$259.7671	$259.77	$259.75	$259.80
Purchase #2	$63.69	12.771%	$71.8238	$71.82	$71.80	$71.80
Purchase #3	$123.96	12.746%	$139.7599	$139.76	$139.75	$139.80
Purchase #4	$192.82	9.716%	$211.5544	$211.55	$211.55	$211.60
Purchase #5	$69.45	12.548%	$78.1646	$78.16	$78.15	$78.20
Purchase #6	$67.59	13.392%	$76.6417	$76.64	$76.65	$76.60
Purchase #7	$17.78	8.382%	$19.2703	$19.27	$19.25	$19.30
7 purchase totals =	$772.01		$856.9818	$856.97	$856.90	$857.10