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	$126.35	7.853%	$136.2723	$136.27	$136.25	$136.30
Purchase #2	$36.50	10.723%	$40.4139	$40.41	$40.40	$40.40
Purchase #3	$175.35	13.621%	$199.2344	$199.23	$199.25	$199.20
Purchase #4	$118.69	9.740%	$130.2504	$130.25	$130.25	$130.30
Purchase #5	$56.74	5.339%	$59.7693	$59.77	$59.75	$59.80
Purchase #6	$224.70	9.555%	$246.1701	$246.17	$246.15	$246.20
Purchase #7	$179.32	13.663%	$203.8205	$203.82	$203.80	$203.80
7 purchase totals =	$917.65		$1,015.9309	$1,015.92	$1,015.85	$1,016.00