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	$46.64	4.229%	$48.6124	$48.61	$48.60	$48.60
Purchase #2	$92.74	11.831%	$103.7121	$103.71	$103.70	$103.70
Purchase #3	$241.78	11.139%	$268.7119	$268.71	$268.70	$268.70
Purchase #4	$203.80	9.346%	$222.8471	$222.85	$222.85	$222.80
Purchase #5	$237.88	3.287%	$245.6991	$245.70	$245.70	$245.70
Purchase #6	$94.59	6.102%	$100.3619	$100.36	$100.35	$100.40
Purchase #7	$13.80	4.427%	$14.4109	$14.41	$14.40	$14.40
7 purchase totals =	$931.23		$1,004.3554	$1,004.35	$1,004.30	$1,004.30