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	$86.89	3.182%	$89.6548	$89.65	$89.65	$89.70
Purchase #2	$40.60	6.738%	$43.3356	$43.34	$43.35	$43.30
Purchase #3	$159.75	5.759%	$168.95	$168.95	$168.95	$169.00
Purchase #4	$189.43	4.873%	$198.6609	$198.66	$198.65	$198.70
Purchase #5	$180.49	6.287%	$191.8374	$191.84	$191.85	$191.80
Purchase #6	$75.78	10.192%	$83.5035	$83.50	$83.50	$83.50
Purchase #7	$196.89	13.687%	$223.8383	$223.84	$223.85	$223.80
7 purchase totals =	$929.83		$999.7805	$999.78	$999.80	$999.80