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	$235.67	12.313%	$264.688	$264.69	$264.70	$264.70
Purchase #2	$84.92	13.523%	$96.4037	$96.40	$96.40	$96.40
Purchase #3	$127.28	9.309%	$139.1285	$139.13	$139.15	$139.10
Purchase #4	$93.38	8.108%	$100.9513	$100.95	$100.95	$101.00
Purchase #5	$107.79	5.127%	$113.3164	$113.32	$113.30	$113.30
Purchase #6	$38.81	4.756%	$40.6558	$40.66	$40.65	$40.70
Purchase #7	$10.45	10.197%	$11.5156	$11.52	$11.50	$11.50
7 purchase totals =	$698.30		$766.6593	$766.67	$766.65	$766.70