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	$20.59	10.661%	$22.7851	$22.79	$22.80	$22.80
Purchase #2	$88.65	11.447%	$98.7978	$98.80	$98.80	$98.80
Purchase #3	$105.75	5.515%	$111.5821	$111.58	$111.60	$111.60
Purchase #4	$233.79	10.805%	$259.051	$259.05	$259.05	$259.10
Purchase #5	$169.40	11.388%	$188.6913	$188.69	$188.70	$188.70
Purchase #6	$33.46	12.678%	$37.7021	$37.70	$37.70	$37.70
Purchase #7	$241.40	7.775%	$260.1689	$260.17	$260.15	$260.20
7 purchase totals =	$893.04		$978.7783	$978.78	$978.80	$978.90