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	$35.90	13.847%	$40.8711	$40.87	$40.85	$40.90
Purchase #2	$105.88	5.658%	$111.8707	$111.87	$111.85	$111.90
Purchase #3	$120.30	5.111%	$126.4485	$126.45	$126.45	$126.40
Purchase #4	$247.72	11.864%	$277.1095	$277.11	$277.10	$277.10
Purchase #5	$118.68	12.568%	$133.5957	$133.60	$133.60	$133.60
Purchase #6	$192.46	3.245%	$198.7053	$198.71	$198.70	$198.70
Purchase #7	$81.95	9.466%	$89.7074	$89.71	$89.70	$89.70
7 purchase totals =	$902.89		$978.3082	$978.32	$978.25	$978.30