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	$122.27	5.112%	$128.5204	$128.52	$128.50	$128.50
Purchase #2	$30.50	5.218%	$32.0915	$32.09	$32.10	$32.10
Purchase #3	$43.77	10.606%	$48.4122	$48.41	$48.40	$48.40
Purchase #4	$108.58	13.385%	$123.1134	$123.11	$123.10	$123.10
Purchase #5	$93.35	11.364%	$103.9583	$103.96	$103.95	$104.00
Purchase #6	$214.52	8.627%	$233.0266	$233.03	$233.05	$233.00
Purchase #7	$248.81	8.630%	$270.2823	$270.28	$270.30	$270.30
7 purchase totals =	$861.80		$939.4047	$939.40	$939.40	$939.40