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	$82.79	9.314%	$90.5011	$90.50	$90.50	$90.50
Purchase #2	$53.53	8.559%	$58.1116	$58.11	$58.10	$58.10
Purchase #3	$86.32	5.178%	$90.7896	$90.79	$90.80	$90.80
Purchase #4	$17.37	3.374%	$17.9561	$17.96	$17.95	$18.00
Purchase #5	$12.44	6.715%	$13.2753	$13.28	$13.30	$13.30
Purchase #6	$31.71	6.242%	$33.6893	$33.69	$33.70	$33.70
Purchase #7	$173.33	10.859%	$192.1519	$192.15	$192.15	$192.20
7 purchase totals =	$457.49		$496.4749	$496.48	$496.50	$496.60