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	$225.92	10.591%	$249.8472	$249.85	$249.85	$249.80
Purchase #2	$84.54	6.209%	$89.7891	$89.79	$89.80	$89.80
Purchase #3	$59.31	3.800%	$61.5638	$61.56	$61.55	$61.60
Purchase #4	$187.86	9.328%	$205.3836	$205.38	$205.40	$205.40
Purchase #5	$47.92	9.798%	$52.6152	$52.62	$52.60	$52.60
Purchase #6	$124.37	3.599%	$128.8461	$128.85	$128.85	$128.80
Purchase #7	$181.80	3.208%	$187.6321	$187.63	$187.65	$187.60
7 purchase totals =	$911.72		$975.6771	$975.68	$975.70	$975.60