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	$232.67	6.107%	$246.8792	$246.88	$246.90	$246.90
Purchase #2	$87.66	3.251%	$90.5098	$90.51	$90.50	$90.50
Purchase #3	$150.96	5.103%	$158.6635	$158.66	$158.65	$158.70
Purchase #4	$133.68	6.597%	$142.4989	$142.50	$142.50	$142.50
Purchase #5	$48.44	13.735%	$55.0932	$55.09	$55.10	$55.10
Purchase #6	$88.31	13.651%	$100.3652	$100.37	$100.35	$100.40
Purchase #7	$172.42	12.735%	$194.3777	$194.38	$194.40	$194.40
7 purchase totals =	$914.14		$988.3875	$988.39	$988.40	$988.50