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	$186.42	9.874%	$204.8271	$204.83	$204.85	$204.80
Purchase #2	$64.38	4.428%	$67.2307	$67.23	$67.25	$67.20
Purchase #3	$210.45	8.409%	$228.1467	$228.15	$228.15	$228.10
Purchase #4	$63.38	4.409%	$66.1744	$66.17	$66.15	$66.20
Purchase #5	$156.31	10.767%	$173.1399	$173.14	$173.15	$173.10
Purchase #6	$24.84	12.377%	$27.9144	$27.91	$27.90	$27.90
Purchase #7	$38.29	10.237%	$42.2097	$42.21	$42.20	$42.20
7 purchase totals =	$744.07		$809.6429	$809.64	$809.65	$809.50