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	$245.34	13.742%	$279.0546	$279.05	$279.05	$279.10
Purchase #2	$86.64	6.872%	$92.5939	$92.59	$92.60	$92.60
Purchase #3	$94.79	8.142%	$102.5078	$102.51	$102.50	$102.50
Purchase #4	$45.56	8.154%	$49.275	$49.28	$49.30	$49.30
Purchase #5	$14.30	7.579%	$15.3838	$15.38	$15.40	$15.40
Purchase #6	$94.92	5.677%	$100.3086	$100.31	$100.30	$100.30
Purchase #7	$113.26	8.681%	$123.0921	$123.09	$123.10	$123.10
7 purchase totals =	$694.81		$762.2158	$762.21	$762.25	$762.30