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	$151.98	10.239%	$167.5412	$167.54	$167.55	$167.50
Purchase #2	$221.25	7.190%	$237.1579	$237.16	$237.15	$237.20
Purchase #3	$78.81	4.795%	$82.5889	$82.59	$82.60	$82.60
Purchase #4	$148.65	12.710%	$167.5434	$167.54	$167.55	$167.50
Purchase #5	$16.74	11.704%	$18.6992	$18.70	$18.70	$18.70
Purchase #6	$72.61	10.125%	$79.9618	$79.96	$79.95	$80.00
Purchase #7	$72.59	12.414%	$81.6013	$81.60	$81.60	$81.60
7 purchase totals =	$762.63		$835.0937	$835.09	$835.10	$835.10