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	$248.73	12.753%	$280.4505	$280.45	$280.45	$280.50
Purchase #2	$108.33	13.819%	$123.3001	$123.30	$123.30	$123.30
Purchase #3	$125.73	5.784%	$133.0022	$133.00	$133.00	$133.00
Purchase #4	$92.59	3.230%	$95.5807	$95.58	$95.60	$95.60
Purchase #5	$80.65	6.139%	$85.6011	$85.60	$85.60	$85.60
Purchase #6	$42.50	8.688%	$46.1924	$46.19	$46.20	$46.20
Purchase #7	$18.41	13.423%	$20.8812	$20.88	$20.90	$20.90
7 purchase totals =	$716.94		$785.0082	$785.00	$785.05	$785.10