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	$119.59	6.469%	$127.3263	$127.33	$127.35	$127.30
Purchase #2	$75.81	3.455%	$78.4292	$78.43	$78.45	$78.40
Purchase #3	$110.67	12.666%	$124.6875	$124.69	$124.70	$124.70
Purchase #4	$115.66	5.671%	$122.2191	$122.22	$122.20	$122.20
Purchase #5	$74.34	12.746%	$83.8154	$83.82	$83.80	$83.80
Purchase #6	$197.99	6.871%	$211.5939	$211.59	$211.60	$211.60
Purchase #7	$236.77	5.540%	$249.8871	$249.89	$249.90	$249.90
7 purchase totals =	$930.83		$997.9585	$997.97	$998.00	$997.90