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	$89.53	10.456%	$98.8913	$98.89	$98.90	$98.90
Purchase #2	$103.97	7.577%	$111.8478	$111.85	$111.85	$111.80
Purchase #3	$196.37	13.308%	$222.5029	$222.50	$222.50	$222.50
Purchase #4	$117.42	12.205%	$131.7511	$131.75	$131.75	$131.80
Purchase #5	$36.29	6.355%	$38.5962	$38.60	$38.60	$38.60
Purchase #6	$127.25	3.425%	$131.6083	$131.61	$131.60	$131.60
Purchase #7	$73.38	7.214%	$78.6736	$78.67	$78.65	$78.70
7 purchase totals =	$744.21		$813.8712	$813.87	$813.85	$813.90