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	$103.89	13.421%	$117.8331	$117.83	$117.85	$117.80
Purchase #2	$99.31	12.324%	$111.549	$111.55	$111.55	$111.50
Purchase #3	$14.82	5.180%	$15.5877	$15.59	$15.60	$15.60
Purchase #4	$156.67	6.407%	$166.7078	$166.71	$166.70	$166.70
Purchase #5	$99.46	12.858%	$112.2486	$112.25	$112.25	$112.20
Purchase #6	$80.90	7.143%	$86.6787	$86.68	$86.70	$86.70
Purchase #7	$151.25	3.291%	$156.2276	$156.23	$156.25	$156.20
7 purchase totals =	$706.30		$766.8325	$766.84	$766.90	$766.70