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	$59.80	12.310%	$67.1614	$67.16	$67.15	$67.20
Purchase #2	$69.89	12.286%	$78.4767	$78.48	$78.50	$78.50
Purchase #3	$138.99	9.263%	$151.8646	$151.86	$151.85	$151.90
Purchase #4	$45.40	10.499%	$50.1665	$50.17	$50.15	$50.20
Purchase #5	$140.92	5.297%	$148.3845	$148.38	$148.40	$148.40
Purchase #6	$233.45	7.384%	$250.6879	$250.69	$250.70	$250.70
Purchase #7	$123.32	4.754%	$129.1826	$129.18	$129.20	$129.20
7 purchase totals =	$811.77		$875.9242	$875.92	$875.95	$876.10