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	$112.94	13.806%	$128.5325	$128.53	$128.55	$128.50
Purchase #2	$152.38	11.757%	$170.2953	$170.30	$170.30	$170.30
Purchase #3	$62.95	13.532%	$71.4684	$71.47	$71.45	$71.50
Purchase #4	$66.71	4.443%	$69.6739	$69.67	$69.65	$69.70
Purchase #5	$241.85	7.457%	$259.8848	$259.88	$259.90	$259.90
Purchase #6	$59.31	3.578%	$61.4321	$61.43	$61.45	$61.40
Purchase #7	$77.82	10.691%	$86.1397	$86.14	$86.15	$86.10
7 purchase totals =	$773.96		$847.4267	$847.42	$847.45	$847.40