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	$129.64	11.610%	$144.6912	$144.69	$144.70	$144.70
Purchase #2	$162.64	5.835%	$172.13	$172.13	$172.15	$172.10
Purchase #3	$151.39	4.374%	$158.0118	$158.01	$158.00	$158.00
Purchase #4	$133.78	3.563%	$138.5466	$138.55	$138.55	$138.50
Purchase #5	$183.33	4.864%	$192.2472	$192.25	$192.25	$192.20
Purchase #6	$73.53	6.546%	$78.3433	$78.34	$78.35	$78.30
Purchase #7	$58.95	11.872%	$65.9485	$65.95	$65.95	$65.90
7 purchase totals =	$893.26		$949.9186	$949.92	$949.95	$949.70