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	$89.88	11.339%	$100.0715	$100.07	$100.05	$100.10
Purchase #2	$171.60	13.269%	$194.3696	$194.37	$194.35	$194.40
Purchase #3	$164.66	13.603%	$187.0587	$187.06	$187.05	$187.10
Purchase #4	$34.28	9.788%	$37.6353	$37.64	$37.65	$37.60
Purchase #5	$78.40	12.404%	$88.1247	$88.12	$88.10	$88.10
Purchase #6	$88.44	11.867%	$98.9352	$98.94	$98.95	$98.90
Purchase #7	$200.70	7.113%	$214.9758	$214.98	$215.00	$215.00
7 purchase totals =	$827.96		$921.1708	$921.18	$921.15	$921.20