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	$91.36	9.467%	$100.0091	$100.01	$100.00	$100.00
Purchase #2	$48.88	5.356%	$51.498	$51.50	$51.50	$51.50
Purchase #3	$151.89	4.602%	$158.88	$158.88	$158.90	$158.90
Purchase #4	$226.71	5.320%	$238.771	$238.77	$238.75	$238.80
Purchase #5	$232.36	7.758%	$250.3865	$250.39	$250.40	$250.40
Purchase #6	$152.74	7.672%	$164.4582	$164.46	$164.45	$164.50
Purchase #7	$174.52	10.400%	$192.6701	$192.67	$192.65	$192.70
7 purchase totals =	$1,078.46		$1,156.6729	$1,156.68	$1,156.65	$1,156.80