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	$52.71	6.602%	$56.1899	$56.19	$56.20	$56.20
Purchase #2	$164.44	7.446%	$176.6842	$176.68	$176.70	$176.70
Purchase #3	$79.81	13.562%	$90.6338	$90.63	$90.65	$90.60
Purchase #4	$171.33	5.481%	$180.7206	$180.72	$180.70	$180.70
Purchase #5	$249.42	10.147%	$274.7286	$274.73	$274.75	$274.70
Purchase #6	$112.42	13.680%	$127.7991	$127.80	$127.80	$127.80
Purchase #7	$109.77	12.244%	$123.2102	$123.21	$123.20	$123.20
7 purchase totals =	$939.90		$1,029.9664	$1,029.96	$1,030.00	$1,029.90