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	$108.81	13.754%	$123.7757	$123.78	$123.80	$123.80
Purchase #2	$196.84	4.319%	$205.3415	$205.34	$205.35	$205.30
Purchase #3	$235.93	9.388%	$258.0791	$258.08	$258.10	$258.10
Purchase #4	$6.54	13.429%	$7.4183	$7.42	$7.40	$7.40
Purchase #5	$113.59	9.355%	$124.2163	$124.22	$124.20	$124.20
Purchase #6	$39.80	13.136%	$45.0281	$45.03	$45.05	$45.00
Purchase #7	$182.77	9.127%	$199.4514	$199.45	$199.45	$199.50
7 purchase totals =	$884.28		$963.3104	$963.32	$963.35	$963.30