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	$80.31	10.834%	$89.0108	$89.01	$89.00	$89.00
Purchase #2	$129.78	9.308%	$141.8599	$141.86	$141.85	$141.90
Purchase #3	$114.55	4.453%	$119.6509	$119.65	$119.65	$119.70
Purchase #4	$205.60	7.355%	$220.7219	$220.72	$220.70	$220.70
Purchase #5	$31.93	4.776%	$33.455	$33.46	$33.45	$33.50
Purchase #6	$101.33	11.351%	$112.832	$112.83	$112.85	$112.80
Purchase #7	$16.61	12.424%	$18.6736	$18.67	$18.65	$18.70
7 purchase totals =	$680.11		$736.2041	$736.20	$736.15	$736.30