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	$10.67	5.591%	$11.2666	$11.27	$11.25	$11.30
Purchase #2	$130.86	4.369%	$136.5773	$136.58	$136.60	$136.60
Purchase #3	$165.30	3.806%	$171.5913	$171.59	$171.60	$171.60
Purchase #4	$238.73	7.545%	$256.7422	$256.74	$256.75	$256.70
Purchase #5	$78.37	9.102%	$85.5032	$85.50	$85.50	$85.50
Purchase #6	$174.59	3.725%	$181.0935	$181.09	$181.10	$181.10
Purchase #7	$127.88	6.722%	$136.4761	$136.48	$136.50	$136.50
7 purchase totals =	$926.40		$979.2502	$979.25	$979.30	$979.30