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	$234.39	6.804%	$250.3379	$250.34	$250.35	$250.30
Purchase #2	$26.27	7.630%	$28.2744	$28.27	$28.25	$28.30
Purchase #3	$52.91	7.567%	$56.9137	$56.91	$56.90	$56.90
Purchase #4	$15.95	10.321%	$17.5962	$17.60	$17.60	$17.60
Purchase #5	$182.70	12.482%	$205.5046	$205.50	$205.50	$205.50
Purchase #6	$142.75	9.410%	$156.1828	$156.18	$156.20	$156.20
Purchase #7	$137.25	13.258%	$155.4466	$155.45	$155.45	$155.40
7 purchase totals =	$792.22		$870.2562	$870.25	$870.25	$870.20