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	$107.62	6.729%	$114.8617	$114.86	$114.85	$114.90
Purchase #2	$193.81	11.403%	$215.9102	$215.91	$215.90	$215.90
Purchase #3	$103.25	8.668%	$112.1997	$112.20	$112.20	$112.20
Purchase #4	$233.79	10.531%	$258.4104	$258.41	$258.40	$258.40
Purchase #5	$116.52	12.561%	$131.1561	$131.16	$131.15	$131.20
Purchase #6	$145.50	9.147%	$158.8089	$158.81	$158.80	$158.80
Purchase #7	$19.82	8.663%	$21.537	$21.54	$21.55	$21.50
7 purchase totals =	$920.31		$1,012.8840	$1,012.89	$1,012.85	$1,012.90