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	$79.62	11.445%	$88.7325	$88.73	$88.75	$88.70
Purchase #2	$208.29	5.228%	$219.1794	$219.18	$219.20	$219.20
Purchase #3	$199.28	11.258%	$221.7149	$221.71	$221.70	$221.70
Purchase #4	$208.65	9.208%	$227.8625	$227.86	$227.85	$227.90
Purchase #5	$89.29	5.143%	$93.8822	$93.88	$93.90	$93.90
Purchase #6	$135.59	6.309%	$144.1444	$144.14	$144.15	$144.10
Purchase #7	$86.78	4.305%	$90.5159	$90.52	$90.50	$90.50
7 purchase totals =	$1,007.50		$1,086.0318	$1,086.02	$1,086.05	$1,086.00