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	$6.96	7.123%	$7.4558	$7.46	$7.45	$7.50
Purchase #2	$209.61	8.574%	$227.582	$227.58	$227.60	$227.60
Purchase #3	$82.61	4.118%	$86.0119	$86.01	$86.00	$86.00
Purchase #4	$85.52	12.393%	$96.1185	$96.12	$96.10	$96.10
Purchase #5	$175.85	6.576%	$187.4139	$187.41	$187.40	$187.40
Purchase #6	$177.67	7.546%	$191.077	$191.08	$191.10	$191.10
Purchase #7	$6.31	8.289%	$6.833	$6.83	$6.85	$6.80
7 purchase totals =	$744.53		$802.4921	$802.49	$802.50	$802.50