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	$77.41	3.795%	$80.3477	$80.35	$80.35	$80.30
Purchase #2	$137.86	4.604%	$144.2071	$144.21	$144.20	$144.20
Purchase #3	$47.71	4.421%	$49.8193	$49.82	$49.80	$49.80
Purchase #4	$20.81	4.780%	$21.8047	$21.80	$21.80	$21.80
Purchase #5	$149.91	13.531%	$170.1943	$170.19	$170.20	$170.20
Purchase #6	$54.70	9.461%	$59.8752	$59.88	$59.90	$59.90
Purchase #7	$197.61	12.554%	$222.418	$222.42	$222.40	$222.40
7 purchase totals =	$686.01		$748.6663	$748.67	$748.65	$748.60