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	$127.79	11.359%	$142.3057	$142.31	$142.30	$142.30
Purchase #2	$75.58	6.449%	$80.4542	$80.45	$80.45	$80.50
Purchase #3	$192.67	10.240%	$212.3994	$212.40	$212.40	$212.40
Purchase #4	$136.56	4.373%	$142.5318	$142.53	$142.55	$142.50
Purchase #5	$150.27	5.408%	$158.3966	$158.40	$158.40	$158.40
Purchase #6	$110.32	9.128%	$120.39	$120.39	$120.40	$120.40
Purchase #7	$43.34	8.145%	$46.87	$46.87	$46.85	$46.90
7 purchase totals =	$836.53		$903.3477	$903.35	$903.35	$903.40