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	$120.71	12.803%	$136.1645	$136.16	$136.15	$136.20
Purchase #2	$152.42	6.165%	$161.8167	$161.82	$161.80	$161.80
Purchase #3	$37.92	8.187%	$41.0245	$41.02	$41.00	$41.00
Purchase #4	$204.27	7.669%	$219.9355	$219.94	$219.95	$219.90
Purchase #5	$13.50	7.588%	$14.5244	$14.52	$14.50	$14.50
Purchase #6	$133.98	7.592%	$144.1518	$144.15	$144.15	$144.20
Purchase #7	$95.50	10.214%	$105.2544	$105.25	$105.25	$105.30
7 purchase totals =	$758.30		$822.8718	$822.86	$822.80	$822.90