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	$109.66	8.436%	$118.9109	$118.91	$118.90	$118.90
Purchase #2	$168.43	10.768%	$186.5665	$186.57	$186.55	$186.60
Purchase #3	$181.58	4.701%	$190.1161	$190.12	$190.10	$190.10
Purchase #4	$84.63	6.724%	$90.3205	$90.32	$90.30	$90.30
Purchase #5	$16.39	10.476%	$18.107	$18.11	$18.10	$18.10
Purchase #6	$146.64	5.299%	$154.4105	$154.41	$154.40	$154.40
Purchase #7	$96.45	9.812%	$105.9137	$105.91	$105.90	$105.90
7 purchase totals =	$803.78		$864.3452	$864.35	$864.25	$864.30