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	$82.86	9.404%	$90.6522	$90.65	$90.65	$90.70
Purchase #2	$241.88	6.808%	$258.3472	$258.35	$258.35	$258.30
Purchase #3	$164.60	10.217%	$181.4172	$181.42	$181.40	$181.40
Purchase #4	$133.76	4.696%	$140.0414	$140.04	$140.05	$140.00
Purchase #5	$91.67	9.340%	$100.232	$100.23	$100.25	$100.20
Purchase #6	$180.92	10.680%	$200.2423	$200.24	$200.25	$200.20
Purchase #7	$235.41	6.129%	$249.8383	$249.84	$249.85	$249.80
7 purchase totals =	$1,131.10		$1,220.7706	$1,220.77	$1,220.80	$1,220.60