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	$237.63	13.869%	$270.5869	$270.59	$270.60	$270.60
Purchase #2	$160.90	12.209%	$180.5443	$180.54	$180.55	$180.50
Purchase #3	$20.87	3.239%	$21.546	$21.55	$21.55	$21.50
Purchase #4	$92.87	4.129%	$96.7046	$96.70	$96.70	$96.70
Purchase #5	$142.80	5.704%	$150.9453	$150.95	$150.95	$150.90
Purchase #6	$96.98	8.775%	$105.49	$105.49	$105.50	$105.50
Purchase #7	$48.44	12.506%	$54.4979	$54.50	$54.50	$54.50
7 purchase totals =	$800.49		$880.3150	$880.32	$880.35	$880.20