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	$204.55	4.428%	$213.6075	$213.61	$213.60	$213.60
Purchase #2	$241.33	3.608%	$250.0372	$250.04	$250.05	$250.00
Purchase #3	$43.44	10.514%	$48.0073	$48.01	$48.00	$48.00
Purchase #4	$250.77	11.672%	$280.0399	$280.04	$280.05	$280.00
Purchase #5	$103.32	8.663%	$112.2706	$112.27	$112.25	$112.30
Purchase #6	$69.44	4.823%	$72.7891	$72.79	$72.80	$72.80
Purchase #7	$87.32	13.140%	$98.7938	$98.79	$98.80	$98.80
7 purchase totals =	$1,000.17		$1,075.5454	$1,075.55	$1,075.55	$1,075.50