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	$77.96	9.206%	$85.137	$85.14	$85.15	$85.10
Purchase #2	$31.67	7.465%	$34.0342	$34.03	$34.05	$34.00
Purchase #3	$93.83	6.644%	$100.0641	$100.06	$100.05	$100.10
Purchase #4	$37.45	3.807%	$38.8757	$38.88	$38.90	$38.90
Purchase #5	$50.90	10.691%	$56.3417	$56.34	$56.35	$56.30
Purchase #6	$12.28	12.508%	$13.816	$13.82	$13.80	$13.80
Purchase #7	$246.49	7.746%	$265.5831	$265.58	$265.60	$265.60
7 purchase totals =	$550.58		$593.8518	$593.85	$593.90	$593.80