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	$190.32	5.569%	$200.9189	$200.92	$200.90	$200.90
Purchase #2	$59.34	10.857%	$65.7825	$65.78	$65.80	$65.80
Purchase #3	$31.72	5.262%	$33.3891	$33.39	$33.40	$33.40
Purchase #4	$12.27	12.778%	$13.8379	$13.84	$13.85	$13.80
Purchase #5	$146.92	3.852%	$152.5794	$152.58	$152.60	$152.60
Purchase #6	$100.70	8.115%	$108.8718	$108.87	$108.85	$108.90
Purchase #7	$62.85	3.323%	$64.9385	$64.94	$64.95	$64.90
7 purchase totals =	$604.12		$640.3181	$640.32	$640.35	$640.30