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	$85.96	3.596%	$89.0511	$89.05	$89.05	$89.10
Purchase #2	$234.99	12.166%	$263.5789	$263.58	$263.60	$263.60
Purchase #3	$138.65	3.180%	$143.0591	$143.06	$143.05	$143.10
Purchase #4	$85.63	8.329%	$92.7621	$92.76	$92.75	$92.80
Purchase #5	$41.52	9.821%	$45.5977	$45.60	$45.60	$45.60
Purchase #6	$223.37	6.458%	$237.7952	$237.80	$237.80	$237.80
Purchase #7	$51.90	5.153%	$54.5744	$54.57	$54.55	$54.60
7 purchase totals =	$862.02		$926.4185	$926.42	$926.40	$926.60