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	$92.55	11.712%	$103.3895	$103.39	$103.40	$103.40
Purchase #2	$171.70	7.684%	$184.8934	$184.89	$184.90	$184.90
Purchase #3	$38.95	4.859%	$40.8426	$40.84	$40.85	$40.80
Purchase #4	$74.76	7.566%	$80.4163	$80.42	$80.40	$80.40
Purchase #5	$246.52	9.787%	$270.6469	$270.65	$270.65	$270.60
Purchase #6	$237.60	4.401%	$248.0568	$248.06	$248.05	$248.10
Purchase #7	$96.36	4.255%	$100.4601	$100.46	$100.45	$100.50
7 purchase totals =	$958.44		$1,028.7056	$1,028.71	$1,028.70	$1,028.70