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	$226.28	8.384%	$245.2513	$245.25	$245.25	$245.30
Purchase #2	$179.77	12.802%	$202.7842	$202.78	$202.80	$202.80
Purchase #3	$70.32	11.510%	$78.4138	$78.41	$78.40	$78.40
Purchase #4	$50.60	11.222%	$56.2783	$56.28	$56.30	$56.30
Purchase #5	$128.92	12.447%	$144.9667	$144.97	$144.95	$145.00
Purchase #6	$20.89	10.396%	$23.0617	$23.06	$23.05	$23.10
Purchase #7	$146.38	4.420%	$152.85	$152.85	$152.85	$152.90
7 purchase totals =	$823.16		$903.6060	$903.60	$903.60	$903.80