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	$36.28	10.611%	$40.1297	$40.13	$40.15	$40.10
Purchase #2	$84.41	12.823%	$95.2339	$95.23	$95.25	$95.20
Purchase #3	$185.51	7.192%	$198.8519	$198.85	$198.85	$198.90
Purchase #4	$249.66	11.747%	$278.9876	$278.99	$279.00	$279.00
Purchase #5	$192.92	8.692%	$209.6886	$209.69	$209.70	$209.70
Purchase #6	$81.83	10.719%	$90.6014	$90.60	$90.60	$90.60
Purchase #7	$137.79	10.617%	$152.4192	$152.42	$152.40	$152.40
7 purchase totals =	$968.40		$1,065.9123	$1,065.91	$1,065.95	$1,065.90