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	$89.72	12.134%	$100.6066	$100.61	$100.60	$100.60
Purchase #2	$98.92	12.649%	$111.4324	$111.43	$111.45	$111.40
Purchase #3	$176.68	9.474%	$193.4187	$193.42	$193.40	$193.40
Purchase #4	$81.93	7.866%	$88.3746	$88.37	$88.35	$88.40
Purchase #5	$246.46	3.425%	$254.9013	$254.90	$254.90	$254.90
Purchase #6	$234.85	12.623%	$264.4951	$264.50	$264.50	$264.50
Purchase #7	$77.56	12.172%	$87.0006	$87.00	$87.00	$87.00
7 purchase totals =	$1,006.12		$1,100.2293	$1,100.23	$1,100.20	$1,100.20