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	$105.55	5.519%	$111.3753	$111.38	$111.40	$111.40
Purchase #2	$230.59	11.490%	$257.0848	$257.08	$257.10	$257.10
Purchase #3	$205.53	8.410%	$222.8151	$222.82	$222.80	$222.80
Purchase #4	$202.67	7.519%	$217.9088	$217.91	$217.90	$217.90
Purchase #5	$7.63	5.716%	$8.0661	$8.07	$8.05	$8.10
Purchase #6	$70.27	8.548%	$76.2767	$76.28	$76.30	$76.30
Purchase #7	$84.65	7.227%	$90.7677	$90.77	$90.75	$90.80
7 purchase totals =	$906.89		$984.2945	$984.31	$984.30	$984.40