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	$155.28	5.783%	$164.2598	$164.26	$164.25	$164.30
Purchase #2	$19.45	11.643%	$21.7146	$21.71	$21.70	$21.70
Purchase #3	$21.32	9.102%	$23.2605	$23.26	$23.25	$23.30
Purchase #4	$153.77	9.626%	$168.5719	$168.57	$168.55	$168.60
Purchase #5	$99.86	12.698%	$112.5402	$112.54	$112.55	$112.50
Purchase #6	$141.74	3.827%	$147.1644	$147.16	$147.15	$147.20
Purchase #7	$172.61	7.495%	$185.5471	$185.55	$185.55	$185.50
7 purchase totals =	$764.03		$823.0585	$823.05	$823.00	$823.10