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	$237.37	3.766%	$246.3094	$246.31	$246.30	$246.30
Purchase #2	$100.88	11.435%	$112.4156	$112.42	$112.40	$112.40
Purchase #3	$163.82	5.685%	$173.1332	$173.13	$173.15	$173.10
Purchase #4	$169.50	13.777%	$192.852	$192.85	$192.85	$192.90
Purchase #5	$48.76	12.583%	$54.8955	$54.90	$54.90	$54.90
Purchase #6	$7.69	7.623%	$8.2762	$8.28	$8.30	$8.30
Purchase #7	$164.48	12.746%	$185.4446	$185.44	$185.45	$185.40
7 purchase totals =	$892.50		$973.3265	$973.33	$973.35	$973.30