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	$109.97	12.439%	$123.6492	$123.65	$123.65	$123.60
Purchase #2	$246.79	13.459%	$280.0055	$280.01	$280.00	$280.00
Purchase #3	$198.46	12.526%	$223.3191	$223.32	$223.30	$223.30
Purchase #4	$134.61	6.742%	$143.6854	$143.69	$143.70	$143.70
Purchase #5	$27.40	7.220%	$29.3783	$29.38	$29.40	$29.40
Purchase #6	$216.41	11.587%	$241.4854	$241.49	$241.50	$241.50
Purchase #7	$140.94	12.828%	$159.0198	$159.02	$159.00	$159.00
7 purchase totals =	$1,074.58		$1,200.5427	$1,200.56	$1,200.55	$1,200.50