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	$160.41	11.731%	$179.2277	$179.23	$179.25	$179.20
Purchase #2	$43.64	3.406%	$45.1264	$45.13	$45.15	$45.10
Purchase #3	$132.52	4.376%	$138.3191	$138.32	$138.30	$138.30
Purchase #4	$122.30	8.193%	$132.32	$132.32	$132.30	$132.30
Purchase #5	$245.66	9.567%	$269.1623	$269.16	$269.15	$269.20
Purchase #6	$196.37	11.151%	$218.2672	$218.27	$218.25	$218.30
Purchase #7	$250.33	10.588%	$276.8349	$276.83	$276.85	$276.80
7 purchase totals =	$1,151.23		$1,259.2576	$1,259.26	$1,259.25	$1,259.20