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	$76.75	8.135%	$82.9936	$82.99	$83.00	$83.00
Purchase #2	$40.52	4.828%	$42.4763	$42.48	$42.50	$42.50
Purchase #3	$27.27	10.680%	$30.1824	$30.18	$30.20	$30.20
Purchase #4	$53.60	10.563%	$59.2618	$59.26	$59.25	$59.30
Purchase #5	$150.87	3.578%	$156.2681	$156.27	$156.25	$156.30
Purchase #6	$59.60	4.768%	$62.4417	$62.44	$62.45	$62.40
Purchase #7	$108.72	12.530%	$122.3426	$122.34	$122.35	$122.30
7 purchase totals =	$517.33		$555.9665	$555.96	$556.00	$556.00