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	$59.39	9.224%	$64.8681	$64.87	$64.85	$64.90
Purchase #2	$167.30	8.488%	$181.5004	$181.50	$181.50	$181.50
Purchase #3	$19.60	3.343%	$20.2552	$20.26	$20.25	$20.30
Purchase #4	$46.45	9.656%	$50.9352	$50.94	$50.95	$50.90
Purchase #5	$223.67	12.203%	$250.9645	$250.96	$250.95	$251.00
Purchase #6	$100.97	6.797%	$107.8329	$107.83	$107.85	$107.80
Purchase #7	$119.80	3.428%	$123.9067	$123.91	$123.90	$123.90
7 purchase totals =	$737.18		$800.2630	$800.27	$800.25	$800.30