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	$82.32	3.314%	$85.0481	$85.05	$85.05	$85.00
Purchase #2	$186.49	10.428%	$205.9372	$205.94	$205.95	$205.90
Purchase #3	$237.54	12.162%	$266.4296	$266.43	$266.45	$266.40
Purchase #4	$12.73	9.168%	$13.8971	$13.90	$13.90	$13.90
Purchase #5	$125.99	4.428%	$131.5688	$131.57	$131.55	$131.60
Purchase #6	$113.59	7.113%	$121.6697	$121.67	$121.65	$121.70
Purchase #7	$139.29	8.362%	$150.9374	$150.94	$150.95	$150.90
7 purchase totals =	$897.95		$975.4879	$975.50	$975.50	$975.40