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	$98.25	13.434%	$111.4489	$111.45	$111.45	$111.40
Purchase #2	$46.81	9.826%	$51.4096	$51.41	$51.40	$51.40
Purchase #3	$180.48	7.431%	$193.8915	$193.89	$193.90	$193.90
Purchase #4	$146.37	12.339%	$164.4306	$164.43	$164.45	$164.40
Purchase #5	$91.29	13.324%	$103.4535	$103.45	$103.45	$103.50
Purchase #6	$62.50	9.470%	$68.4188	$68.42	$68.40	$68.40
Purchase #7	$146.25	8.562%	$158.7719	$158.77	$158.75	$158.80
7 purchase totals =	$771.95		$851.8248	$851.82	$851.80	$851.80