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	$51.39	9.175%	$56.105	$56.11	$56.10	$56.10
Purchase #2	$138.35	13.187%	$156.5942	$156.59	$156.60	$156.60
Purchase #3	$144.26	7.821%	$155.5426	$155.54	$155.55	$155.50
Purchase #4	$124.45	9.767%	$136.605	$136.61	$136.60	$136.60
Purchase #5	$178.98	6.678%	$190.9323	$190.93	$190.95	$190.90
Purchase #6	$142.58	7.245%	$152.9099	$152.91	$152.90	$152.90
Purchase #7	$210.67	6.211%	$223.7547	$223.75	$223.75	$223.80
7 purchase totals =	$990.68		$1,072.4437	$1,072.44	$1,072.45	$1,072.40