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	$39.27	8.259%	$42.5133	$42.51	$42.50	$42.50
Purchase #2	$48.68	7.784%	$52.4693	$52.47	$52.45	$52.50
Purchase #3	$108.38	10.201%	$119.4358	$119.44	$119.45	$119.40
Purchase #4	$166.88	4.179%	$173.8539	$173.85	$173.85	$173.90
Purchase #5	$152.83	11.151%	$169.8721	$169.87	$169.85	$169.90
Purchase #6	$246.31	12.849%	$277.9584	$277.96	$277.95	$278.00
Purchase #7	$116.34	7.629%	$125.2156	$125.22	$125.20	$125.20
7 purchase totals =	$878.69		$961.3184	$961.32	$961.25	$961.40