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	$147.54	13.778%	$167.8681	$167.87	$167.85	$167.90
Purchase #2	$59.63	12.471%	$67.0665	$67.07	$67.05	$67.10
Purchase #3	$105.69	5.158%	$111.1415	$111.14	$111.15	$111.10
Purchase #4	$22.38	12.282%	$25.1287	$25.13	$25.15	$25.10
Purchase #5	$176.79	6.726%	$188.6809	$188.68	$188.70	$188.70
Purchase #6	$50.93	9.461%	$55.7485	$55.75	$55.75	$55.70
Purchase #7	$40.92	8.658%	$44.4629	$44.46	$44.45	$44.50
7 purchase totals =	$603.88		$660.0971	$660.10	$660.10	$660.10