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	$26.55	12.697%	$29.9211	$29.92	$29.90	$29.90
Purchase #2	$49.73	8.169%	$53.7924	$53.79	$53.80	$53.80
Purchase #3	$40.79	5.602%	$43.0751	$43.08	$43.10	$43.10
Purchase #4	$69.37	4.495%	$72.4882	$72.49	$72.50	$72.50
Purchase #5	$57.53	8.869%	$62.6323	$62.63	$62.65	$62.60
Purchase #6	$223.96	5.609%	$236.5219	$236.52	$236.50	$236.50
Purchase #7	$155.95	6.860%	$166.6482	$166.65	$166.65	$166.60
7 purchase totals =	$623.88		$665.0792	$665.08	$665.10	$665.00