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	$243.52	10.709%	$269.5986	$269.60	$269.60	$269.60
Purchase #2	$206.48	8.833%	$224.7184	$224.72	$224.70	$224.70
Purchase #3	$125.63	10.575%	$138.9154	$138.92	$138.90	$138.90
Purchase #4	$182.37	4.868%	$191.2478	$191.25	$191.25	$191.20
Purchase #5	$249.54	9.181%	$272.4503	$272.45	$272.45	$272.50
Purchase #6	$75.45	3.748%	$78.2779	$78.28	$78.30	$78.30
Purchase #7	$69.41	13.199%	$78.5714	$78.57	$78.55	$78.60
7 purchase totals =	$1,152.40		$1,253.7798	$1,253.79	$1,253.75	$1,253.80