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	$5.63	11.865%	$6.298	$6.30	$6.30	$6.30
Purchase #2	$148.64	9.432%	$162.6597	$162.66	$162.65	$162.70
Purchase #3	$39.60	5.641%	$41.8338	$41.83	$41.85	$41.80
Purchase #4	$111.70	9.567%	$122.3863	$122.39	$122.40	$122.40
Purchase #5	$43.87	3.711%	$45.498	$45.50	$45.50	$45.50
Purchase #6	$82.62	6.678%	$88.1374	$88.14	$88.15	$88.10
Purchase #7	$60.61	8.581%	$65.8109	$65.81	$65.80	$65.80
7 purchase totals =	$492.67		$532.6241	$532.63	$532.65	$532.60