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	$166.38	11.346%	$185.2575	$185.26	$185.25	$185.30
Purchase #2	$119.45	7.490%	$128.3968	$128.40	$128.40	$128.40
Purchase #3	$145.53	5.336%	$153.2955	$153.30	$153.30	$153.30
Purchase #4	$12.86	4.394%	$13.4251	$13.43	$13.45	$13.40
Purchase #5	$90.79	10.187%	$100.0388	$100.04	$100.05	$100.00
Purchase #6	$224.84	11.831%	$251.4408	$251.44	$251.45	$251.40
Purchase #7	$25.59	6.572%	$27.2718	$27.27	$27.25	$27.30
7 purchase totals =	$785.44		$859.1263	$859.14	$859.15	$859.10