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	$42.38	8.211%	$45.8598	$45.86	$45.85	$45.90
Purchase #2	$87.53	13.359%	$99.2231	$99.22	$99.20	$99.20
Purchase #3	$154.42	6.524%	$164.4944	$164.49	$164.50	$164.50
Purchase #4	$79.68	6.773%	$85.0767	$85.08	$85.10	$85.10
Purchase #5	$46.67	7.261%	$50.0587	$50.06	$50.05	$50.10
Purchase #6	$247.45	9.788%	$271.6704	$271.67	$271.65	$271.70
Purchase #7	$186.93	6.545%	$199.1646	$199.16	$199.15	$199.20
7 purchase totals =	$845.06		$915.5477	$915.54	$915.50	$915.70