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	$111.49	11.618%	$124.4429	$124.44	$124.45	$124.40
Purchase #2	$30.87	6.711%	$32.9417	$32.94	$32.95	$32.90
Purchase #3	$208.56	9.832%	$229.0656	$229.07	$229.05	$229.10
Purchase #4	$150.77	5.415%	$158.9342	$158.93	$158.95	$158.90
Purchase #5	$112.35	13.545%	$127.5678	$127.57	$127.55	$127.60
Purchase #6	$185.33	13.299%	$209.977	$209.98	$210.00	$210.00
Purchase #7	$13.58	12.172%	$15.233	$15.23	$15.25	$15.20
7 purchase totals =	$812.95		$898.1622	$898.16	$898.20	$898.10