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	$206.25	9.843%	$226.5512	$226.55	$226.55	$226.60
Purchase #2	$98.37	7.624%	$105.8697	$105.87	$105.85	$105.90
Purchase #3	$80.98	3.513%	$83.8248	$83.82	$83.80	$83.80
Purchase #4	$249.81	7.569%	$268.7181	$268.72	$268.70	$268.70
Purchase #5	$42.35	8.553%	$45.9722	$45.97	$45.95	$46.00
Purchase #6	$94.64	9.439%	$103.5731	$103.57	$103.55	$103.60
Purchase #7	$51.45	10.637%	$56.9227	$56.92	$56.90	$56.90
7 purchase totals =	$823.85		$891.4318	$891.42	$891.30	$891.50