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	$24.38	11.493%	$27.182	$27.18	$27.20	$27.20
Purchase #2	$55.80	12.450%	$62.7471	$62.75	$62.75	$62.70
Purchase #3	$75.33	13.225%	$85.2924	$85.29	$85.30	$85.30
Purchase #4	$237.34	7.426%	$254.9649	$254.96	$254.95	$255.00
Purchase #5	$17.27	9.140%	$18.8485	$18.85	$18.85	$18.80
Purchase #6	$90.96	8.739%	$98.909	$98.91	$98.90	$98.90
Purchase #7	$94.79	5.121%	$99.6442	$99.64	$99.65	$99.60
7 purchase totals =	$595.87		$647.5881	$647.58	$647.60	$647.50