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	$90.50	10.803%	$100.2767	$100.28	$100.30	$100.30
Purchase #2	$116.96	7.152%	$125.325	$125.33	$125.35	$125.30
Purchase #3	$129.70	10.587%	$143.4313	$143.43	$143.45	$143.40
Purchase #4	$214.71	6.138%	$227.8889	$227.89	$227.90	$227.90
Purchase #5	$75.33	4.256%	$78.536	$78.54	$78.55	$78.50
Purchase #6	$216.25	5.704%	$228.5849	$228.58	$228.60	$228.60
Purchase #7	$183.79	7.519%	$197.6092	$197.61	$197.60	$197.60
7 purchase totals =	$1,027.24		$1,101.6520	$1,101.66	$1,101.75	$1,101.60