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	$104.61	3.238%	$107.9973	$108.00	$108.00	$108.00
Purchase #2	$234.45	3.148%	$241.8305	$241.83	$241.85	$241.80
Purchase #3	$88.61	12.669%	$99.836	$99.84	$99.85	$99.80
Purchase #4	$237.68	4.530%	$248.4469	$248.45	$248.45	$248.40
Purchase #5	$77.83	11.527%	$86.8015	$86.80	$86.80	$86.80
Purchase #6	$124.81	6.147%	$132.4821	$132.48	$132.50	$132.50
Purchase #7	$148.88	13.652%	$169.2051	$169.21	$169.20	$169.20
7 purchase totals =	$1,016.87		$1,086.5994	$1,086.61	$1,086.65	$1,086.50