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	$231.68	11.185%	$257.5934	$257.59	$257.60	$257.60
Purchase #2	$97.70	3.766%	$101.3794	$101.38	$101.40	$101.40
Purchase #3	$168.66	6.113%	$178.9702	$178.97	$178.95	$179.00
Purchase #4	$169.98	7.336%	$182.4497	$182.45	$182.45	$182.40
Purchase #5	$233.51	12.857%	$263.5324	$263.53	$263.55	$263.50
Purchase #6	$67.25	4.324%	$70.1579	$70.16	$70.15	$70.20
Purchase #7	$169.41	12.386%	$190.3931	$190.39	$190.40	$190.40
7 purchase totals =	$1,138.19		$1,244.4761	$1,244.47	$1,244.50	$1,244.50