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	$95.54	13.624%	$108.5564	$108.56	$108.55	$108.60
Purchase #2	$213.28	7.709%	$229.7218	$229.72	$229.70	$229.70
Purchase #3	$78.78	13.629%	$89.5169	$89.52	$89.50	$89.50
Purchase #4	$184.35	3.208%	$190.2639	$190.26	$190.25	$190.30
Purchase #5	$82.83	6.194%	$87.9605	$87.96	$87.95	$88.00
Purchase #6	$79.48	12.750%	$89.6137	$89.61	$89.60	$89.60
Purchase #7	$124.76	3.652%	$129.3162	$129.32	$129.30	$129.30
7 purchase totals =	$859.02		$924.9494	$924.95	$924.85	$925.00