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	$6.32	3.213%	$6.5231	$6.52	$6.50	$6.50
Purchase #2	$242.37	8.676%	$263.398	$263.40	$263.40	$263.40
Purchase #3	$82.82	9.872%	$90.996	$91.00	$91.00	$91.00
Purchase #4	$38.94	11.785%	$43.5291	$43.53	$43.55	$43.50
Purchase #5	$143.92	4.772%	$150.7879	$150.79	$150.80	$150.80
Purchase #6	$40.52	7.189%	$43.433	$43.43	$43.45	$43.40
Purchase #7	$177.28	3.549%	$183.5717	$183.57	$183.55	$183.60
7 purchase totals =	$732.17		$782.2388	$782.24	$782.25	$782.20