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	$229.67	8.182%	$248.4616	$248.46	$248.45	$248.50
Purchase #2	$77.25	3.795%	$80.1816	$80.18	$80.20	$80.20
Purchase #3	$78.98	13.805%	$89.8832	$89.88	$89.90	$89.90
Purchase #4	$98.37	10.677%	$108.873	$108.87	$108.85	$108.90
Purchase #5	$173.73	8.757%	$188.9435	$188.94	$188.95	$188.90
Purchase #6	$142.28	6.377%	$151.3532	$151.35	$151.35	$151.40
Purchase #7	$170.51	12.555%	$191.9175	$191.92	$191.90	$191.90
7 purchase totals =	$970.79		$1,059.6136	$1,059.60	$1,059.60	$1,059.70