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	$135.55	3.173%	$139.851	$139.85	$139.85	$139.90
Purchase #2	$40.72	11.850%	$45.5453	$45.55	$45.55	$45.50
Purchase #3	$167.30	10.441%	$184.7678	$184.77	$184.75	$184.80
Purchase #4	$180.95	3.247%	$186.8254	$186.83	$186.85	$186.80
Purchase #5	$42.46	4.312%	$44.2909	$44.29	$44.30	$44.30
Purchase #6	$36.36	8.631%	$39.4982	$39.50	$39.50	$39.50
Purchase #7	$154.70	4.156%	$161.1293	$161.13	$161.15	$161.10
7 purchase totals =	$758.04		$801.9079	$801.92	$801.95	$801.90