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	$97.78	11.852%	$109.3689	$109.37	$109.35	$109.40
Purchase #2	$178.42	4.743%	$186.8825	$186.88	$186.90	$186.90
Purchase #3	$12.26	4.638%	$12.8286	$12.83	$12.85	$12.80
Purchase #4	$142.74	4.325%	$148.9135	$148.91	$148.90	$148.90
Purchase #5	$84.56	6.641%	$90.1756	$90.18	$90.20	$90.20
Purchase #6	$81.79	13.702%	$92.9969	$93.00	$93.00	$93.00
Purchase #7	$150.39	9.455%	$164.6094	$164.61	$164.60	$164.60
7 purchase totals =	$747.94		$805.7754	$805.78	$805.80	$805.80