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	$23.89	11.241%	$26.5755	$26.58	$26.60	$26.60
Purchase #2	$29.90	7.831%	$32.2415	$32.24	$32.25	$32.20
Purchase #3	$7.54	3.798%	$7.8264	$7.83	$7.85	$7.80
Purchase #4	$51.40	5.169%	$54.0569	$54.06	$54.05	$54.10
Purchase #5	$248.85	4.305%	$259.563	$259.56	$259.55	$259.60
Purchase #6	$65.29	12.867%	$73.6909	$73.69	$73.70	$73.70
Purchase #7	$76.47	7.104%	$81.9024	$81.90	$81.90	$81.90
7 purchase totals =	$503.34		$535.8566	$535.86	$535.90	$535.90