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	$102.75	13.306%	$116.4219	$116.42	$116.40	$116.40
Purchase #2	$159.70	12.579%	$179.7887	$179.79	$179.80	$179.80
Purchase #3	$175.80	7.600%	$189.1608	$189.16	$189.15	$189.20
Purchase #4	$141.82	10.706%	$157.0032	$157.00	$157.00	$157.00
Purchase #5	$56.83	9.385%	$62.1635	$62.16	$62.15	$62.20
Purchase #6	$169.59	12.480%	$190.7548	$190.75	$190.75	$190.80
Purchase #7	$95.89	11.697%	$107.1063	$107.11	$107.10	$107.10
7 purchase totals =	$902.38		$1,002.3992	$1,002.39	$1,002.35	$1,002.50