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	$133.51	8.523%	$144.8891	$144.89	$144.90	$144.90
Purchase #2	$29.76	5.115%	$31.2822	$31.28	$31.30	$31.30
Purchase #3	$112.99	5.298%	$118.9762	$118.98	$119.00	$119.00
Purchase #4	$51.37	11.673%	$57.3664	$57.37	$57.35	$57.40
Purchase #5	$90.76	13.872%	$103.3502	$103.35	$103.35	$103.40
Purchase #6	$185.67	6.222%	$197.2224	$197.22	$197.20	$197.20
Purchase #7	$81.92	4.812%	$85.862	$85.86	$85.85	$85.90
7 purchase totals =	$685.98		$738.9485	$738.95	$738.95	$739.10