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	$179.43	6.252%	$190.648	$190.65	$190.65	$190.60
Purchase #2	$35.80	13.591%	$40.6656	$40.67	$40.65	$40.70
Purchase #3	$100.93	8.375%	$109.3829	$109.38	$109.40	$109.40
Purchase #4	$56.31	9.713%	$61.7794	$61.78	$61.80	$61.80
Purchase #5	$110.25	8.110%	$119.1913	$119.19	$119.20	$119.20
Purchase #6	$138.33	3.712%	$143.4648	$143.46	$143.45	$143.50
Purchase #7	$143.58	7.438%	$154.2595	$154.26	$154.25	$154.30
7 purchase totals =	$764.63		$819.3915	$819.39	$819.40	$819.50