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	$38.52	6.151%	$40.8894	$40.89	$40.90	$40.90
Purchase #2	$221.70	7.492%	$238.3098	$238.31	$238.30	$238.30
Purchase #3	$72.81	3.782%	$75.5637	$75.56	$75.55	$75.60
Purchase #4	$149.78	9.250%	$163.6347	$163.63	$163.65	$163.60
Purchase #5	$227.94	12.234%	$255.8262	$255.83	$255.85	$255.80
Purchase #6	$31.88	4.120%	$33.1935	$33.19	$33.20	$33.20
Purchase #7	$53.76	10.504%	$59.407	$59.41	$59.40	$59.40
7 purchase totals =	$796.39		$866.8243	$866.82	$866.85	$866.80