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	$203.35	8.792%	$221.2285	$221.23	$221.25	$221.20
Purchase #2	$72.33	10.303%	$79.7822	$79.78	$79.80	$79.80
Purchase #3	$56.71	6.832%	$60.5844	$60.58	$60.60	$60.60
Purchase #4	$57.28	3.836%	$59.4773	$59.48	$59.50	$59.50
Purchase #5	$156.75	4.795%	$164.2662	$164.27	$164.25	$164.30
Purchase #6	$41.82	11.240%	$46.5206	$46.52	$46.50	$46.50
Purchase #7	$199.75	8.150%	$216.0296	$216.03	$216.05	$216.00
7 purchase totals =	$787.99		$847.8888	$847.89	$847.95	$847.90