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	$240.55	6.714%	$256.7005	$256.70	$256.70	$256.70
Purchase #2	$83.52	9.233%	$91.2314	$91.23	$91.25	$91.20
Purchase #3	$48.28	4.605%	$50.5033	$50.50	$50.50	$50.50
Purchase #4	$86.72	4.168%	$90.3345	$90.33	$90.35	$90.30
Purchase #5	$102.42	4.289%	$106.8128	$106.81	$106.80	$106.80
Purchase #6	$41.97	3.607%	$43.4839	$43.48	$43.50	$43.50
Purchase #7	$22.30	8.185%	$24.1253	$24.13	$24.15	$24.10
7 purchase totals =	$625.76		$663.1917	$663.18	$663.25	$663.10