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	$130.53	9.190%	$142.5257	$142.53	$142.55	$142.50
Purchase #2	$29.94	5.712%	$31.6502	$31.65	$31.65	$31.70
Purchase #3	$220.60	4.459%	$230.4366	$230.44	$230.45	$230.40
Purchase #4	$119.28	11.109%	$132.5308	$132.53	$132.55	$132.50
Purchase #5	$138.85	3.167%	$143.2474	$143.25	$143.25	$143.20
Purchase #6	$187.62	9.228%	$204.9336	$204.93	$204.95	$204.90
Purchase #7	$40.69	5.476%	$42.9182	$42.92	$42.90	$42.90
7 purchase totals =	$867.51		$928.2425	$928.25	$928.30	$928.10