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	$110.70	11.757%	$123.715	$123.72	$123.70	$123.70
Purchase #2	$112.42	13.490%	$127.5855	$127.59	$127.60	$127.60
Purchase #3	$130.50	11.403%	$145.3809	$145.38	$145.40	$145.40
Purchase #4	$180.92	9.351%	$197.8378	$197.84	$197.85	$197.80
Purchase #5	$113.91	4.380%	$118.8993	$118.90	$118.90	$118.90
Purchase #6	$226.52	13.280%	$256.6019	$256.60	$256.60	$256.60
Purchase #7	$105.30	7.638%	$113.3428	$113.34	$113.35	$113.30
7 purchase totals =	$980.27		$1,083.3632	$1,083.37	$1,083.40	$1,083.30