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	$78.53	13.819%	$89.3821	$89.38	$89.40	$89.40
Purchase #2	$156.51	3.554%	$162.0724	$162.07	$162.05	$162.10
Purchase #3	$126.28	3.673%	$130.9183	$130.92	$130.90	$130.90
Purchase #4	$123.41	3.550%	$127.7911	$127.79	$127.80	$127.80
Purchase #5	$7.50	8.460%	$8.1345	$8.13	$8.15	$8.10
Purchase #6	$88.97	12.225%	$99.8466	$99.85	$99.85	$99.80
Purchase #7	$122.68	12.477%	$137.9868	$137.99	$138.00	$138.00
7 purchase totals =	$703.88		$756.1318	$756.13	$756.15	$756.10