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	$197.79	4.344%	$206.382	$206.38	$206.40	$206.40
Purchase #2	$39.82	11.483%	$44.3925	$44.39	$44.40	$44.40
Purchase #3	$224.80	4.205%	$234.2528	$234.25	$234.25	$234.30
Purchase #4	$116.81	9.508%	$127.9163	$127.92	$127.90	$127.90
Purchase #5	$40.38	5.787%	$42.7168	$42.72	$42.70	$42.70
Purchase #6	$37.88	11.812%	$42.3544	$42.35	$42.35	$42.40
Purchase #7	$125.69	5.760%	$132.9297	$132.93	$132.95	$132.90
7 purchase totals =	$783.17		$830.9445	$830.94	$830.95	$831.00