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	$210.93	13.124%	$238.6125	$238.61	$238.60	$238.60
Purchase #2	$199.74	6.223%	$212.1698	$212.17	$212.15	$212.20
Purchase #3	$176.55	13.649%	$200.6473	$200.65	$200.65	$200.60
Purchase #4	$81.51	9.371%	$89.1483	$89.15	$89.15	$89.10
Purchase #5	$51.30	5.152%	$53.943	$53.94	$53.95	$53.90
Purchase #6	$19.60	10.687%	$21.6947	$21.69	$21.70	$21.70
Purchase #7	$5.86	12.671%	$6.6025	$6.60	$6.60	$6.60
7 purchase totals =	$745.49		$822.8181	$822.81	$822.80	$822.70