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	$250.89	12.833%	$283.0867	$283.09	$283.10	$283.10
Purchase #2	$33.89	10.279%	$37.3736	$37.37	$37.35	$37.40
Purchase #3	$52.57	13.391%	$59.6096	$59.61	$59.60	$59.60
Purchase #4	$204.96	9.574%	$224.5829	$224.58	$224.60	$224.60
Purchase #5	$129.33	5.646%	$136.632	$136.63	$136.65	$136.60
Purchase #6	$10.39	11.205%	$11.5542	$11.55	$11.55	$11.60
Purchase #7	$123.90	8.421%	$134.3336	$134.33	$134.35	$134.30
7 purchase totals =	$805.93		$887.1726	$887.16	$887.20	$887.20