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	$108.41	11.139%	$120.4858	$120.49	$120.50	$120.50
Purchase #2	$120.57	5.418%	$127.1025	$127.10	$127.10	$127.10
Purchase #3	$110.25	5.842%	$116.6908	$116.69	$116.70	$116.70
Purchase #4	$140.65	5.159%	$147.9061	$147.91	$147.90	$147.90
Purchase #5	$57.73	12.759%	$65.0958	$65.10	$65.10	$65.10
Purchase #6	$81.98	4.768%	$85.8888	$85.89	$85.90	$85.90
Purchase #7	$127.94	8.191%	$138.4196	$138.42	$138.40	$138.40
7 purchase totals =	$747.53		$801.5894	$801.60	$801.60	$801.60