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	$86.37	7.203%	$92.5912	$92.59	$92.60	$92.60
Purchase #2	$152.76	3.702%	$158.4152	$158.42	$158.40	$158.40
Purchase #3	$180.89	10.608%	$200.0788	$200.08	$200.10	$200.10
Purchase #4	$250.35	11.236%	$278.4793	$278.48	$278.50	$278.50
Purchase #5	$21.72	10.158%	$23.9263	$23.93	$23.95	$23.90
Purchase #6	$209.40	5.652%	$221.2353	$221.24	$221.25	$221.20
Purchase #7	$112.49	3.393%	$116.3068	$116.31	$116.30	$116.30
7 purchase totals =	$1,013.98		$1,091.0329	$1,091.05	$1,091.10	$1,091.00