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	$20.50	5.535%	$21.6347	$21.63	$21.65	$21.60
Purchase #2	$137.69	13.326%	$156.0386	$156.04	$156.05	$156.00
Purchase #3	$105.92	6.377%	$112.6745	$112.67	$112.65	$112.70
Purchase #4	$183.98	6.811%	$196.5109	$196.51	$196.50	$196.50
Purchase #5	$54.82	4.123%	$57.0802	$57.08	$57.10	$57.10
Purchase #6	$132.98	12.604%	$149.7408	$149.74	$149.75	$149.70
Purchase #7	$154.65	8.269%	$167.438	$167.44	$167.45	$167.40
7 purchase totals =	$790.54		$861.1177	$861.11	$861.15	$861.00