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	$82.80	8.853%	$90.1303	$90.13	$90.15	$90.10
Purchase #2	$190.38	12.148%	$213.5074	$213.51	$213.50	$213.50
Purchase #3	$200.80	9.160%	$219.1933	$219.19	$219.20	$219.20
Purchase #4	$158.25	3.764%	$164.2065	$164.21	$164.20	$164.20
Purchase #5	$101.81	9.305%	$111.2834	$111.28	$111.30	$111.30
Purchase #6	$81.47	12.415%	$91.5845	$91.58	$91.60	$91.60
Purchase #7	$215.65	7.527%	$231.882	$231.88	$231.90	$231.90
7 purchase totals =	$1,031.16		$1,121.7874	$1,121.78	$1,121.85	$1,121.80