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	$242.76	5.391%	$255.8472	$255.85	$255.85	$255.80
Purchase #2	$173.35	10.313%	$191.2276	$191.23	$191.25	$191.20
Purchase #3	$149.28	12.587%	$168.0699	$168.07	$168.05	$168.10
Purchase #4	$145.98	10.222%	$160.9021	$160.90	$160.90	$160.90
Purchase #5	$75.53	11.188%	$83.9803	$83.98	$84.00	$84.00
Purchase #6	$72.52	13.236%	$82.1187	$82.12	$82.10	$82.10
Purchase #7	$46.83	10.150%	$51.5832	$51.58	$51.60	$51.60
7 purchase totals =	$906.25		$993.7290	$993.73	$993.75	$993.70