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	$7.53	4.660%	$7.8809	$7.88	$7.90	$7.90
Purchase #2	$228.78	11.485%	$255.0554	$255.06	$255.05	$255.10
Purchase #3	$196.49	4.160%	$204.664	$204.66	$204.65	$204.70
Purchase #4	$132.64	4.703%	$138.8781	$138.88	$138.90	$138.90
Purchase #5	$88.73	9.207%	$96.8994	$96.90	$96.90	$96.90
Purchase #6	$44.58	10.369%	$49.2025	$49.20	$49.20	$49.20
Purchase #7	$104.50	6.526%	$111.3197	$111.32	$111.30	$111.30
7 purchase totals =	$803.25		$863.9000	$863.90	$863.90	$864.00