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	$159.75	5.237%	$168.1161	$168.12	$168.10	$168.10
Purchase #2	$127.47	3.856%	$132.3852	$132.39	$132.40	$132.40
Purchase #3	$87.84	10.161%	$96.7654	$96.77	$96.75	$96.80
Purchase #4	$140.61	6.776%	$150.1377	$150.14	$150.15	$150.10
Purchase #5	$78.68	9.238%	$85.9485	$85.95	$85.95	$85.90
Purchase #6	$18.44	7.853%	$19.8881	$19.89	$19.90	$19.90
Purchase #7	$51.69	9.620%	$56.6626	$56.66	$56.65	$56.70
7 purchase totals =	$664.48		$709.9036	$709.92	$709.90	$709.90