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	$170.26	7.205%	$182.5272	$182.53	$182.55	$182.50
Purchase #2	$215.58	12.180%	$241.8376	$241.84	$241.85	$241.80
Purchase #3	$153.92	5.665%	$162.6396	$162.64	$162.65	$162.60
Purchase #4	$33.52	11.809%	$37.4784	$37.48	$37.50	$37.50
Purchase #5	$92.31	6.635%	$98.4348	$98.43	$98.45	$98.40
Purchase #6	$46.97	8.609%	$51.0136	$51.01	$51.00	$51.00
Purchase #7	$169.39	9.538%	$185.5464	$185.55	$185.55	$185.50
7 purchase totals =	$881.95		$959.4776	$959.48	$959.55	$959.30