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	$49.53	6.731%	$52.8639	$52.86	$52.85	$52.90
Purchase #2	$192.35	10.645%	$212.8257	$212.83	$212.85	$212.80
Purchase #3	$40.64	6.195%	$43.1576	$43.16	$43.15	$43.20
Purchase #4	$34.68	9.243%	$37.8855	$37.89	$37.90	$37.90
Purchase #5	$107.89	5.867%	$114.2199	$114.22	$114.20	$114.20
Purchase #6	$199.79	5.671%	$211.1201	$211.12	$211.10	$211.10
Purchase #7	$196.35	6.341%	$208.8006	$208.80	$208.80	$208.80
7 purchase totals =	$821.23		$880.8733	$880.88	$880.85	$880.90