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	$150.51	6.515%	$160.3157	$160.32	$160.30	$160.30
Purchase #2	$70.82	13.525%	$80.3984	$80.40	$80.40	$80.40
Purchase #3	$35.49	4.430%	$37.0622	$37.06	$37.05	$37.10
Purchase #4	$34.61	11.825%	$38.7026	$38.70	$38.70	$38.70
Purchase #5	$213.54	3.675%	$221.3876	$221.39	$221.40	$221.40
Purchase #6	$104.25	7.398%	$111.9624	$111.96	$111.95	$112.00
Purchase #7	$223.84	12.842%	$252.5855	$252.59	$252.60	$252.60
7 purchase totals =	$833.06		$902.4144	$902.42	$902.40	$902.50