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	$138.83	4.250%	$144.7303	$144.73	$144.75	$144.70
Purchase #2	$18.47	9.591%	$20.2415	$20.24	$20.25	$20.20
Purchase #3	$108.81	3.859%	$113.009	$113.01	$113.00	$113.00
Purchase #4	$96.51	6.478%	$102.7619	$102.76	$102.75	$102.80
Purchase #5	$170.78	4.574%	$178.5915	$178.59	$178.60	$178.60
Purchase #6	$86.72	4.360%	$90.501	$90.50	$90.50	$90.50
Purchase #7	$118.31	12.516%	$133.1177	$133.12	$133.10	$133.10
7 purchase totals =	$738.43		$782.9529	$782.95	$782.95	$782.90