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	$62.86	6.720%	$67.0842	$67.08	$67.10	$67.10
Purchase #2	$165.37	10.587%	$182.8777	$182.88	$182.90	$182.90
Purchase #3	$155.65	5.552%	$164.2917	$164.29	$164.30	$164.30
Purchase #4	$41.68	4.130%	$43.4014	$43.40	$43.40	$43.40
Purchase #5	$126.51	8.841%	$137.6947	$137.69	$137.70	$137.70
Purchase #6	$138.87	12.582%	$156.3426	$156.34	$156.35	$156.30
Purchase #7	$55.81	7.169%	$59.811	$59.81	$59.80	$59.80
7 purchase totals =	$746.75		$811.5033	$811.49	$811.55	$811.50