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	$52.30	13.636%	$59.4316	$59.43	$59.45	$59.40
Purchase #2	$123.56	3.577%	$127.9797	$127.98	$128.00	$128.00
Purchase #3	$205.39	5.422%	$216.5262	$216.53	$216.55	$216.50
Purchase #4	$24.38	11.465%	$27.1752	$27.18	$27.20	$27.20
Purchase #5	$164.50	11.232%	$182.9766	$182.98	$183.00	$183.00
Purchase #6	$47.59	10.320%	$52.5013	$52.50	$52.50	$52.50
Purchase #7	$96.92	13.352%	$109.8608	$109.86	$109.85	$109.90
7 purchase totals =	$714.64		$776.4514	$776.46	$776.55	$776.50