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	$109.46	13.152%	$123.8562	$123.86	$123.85	$123.90
Purchase #2	$122.67	10.767%	$135.8779	$135.88	$135.90	$135.90
Purchase #3	$75.58	8.587%	$82.0701	$82.07	$82.05	$82.10
Purchase #4	$243.50	8.339%	$263.8055	$263.81	$263.80	$263.80
Purchase #5	$75.52	9.874%	$82.9768	$82.98	$83.00	$83.00
Purchase #6	$133.63	12.452%	$150.2696	$150.27	$150.25	$150.30
Purchase #7	$222.84	11.457%	$248.3708	$248.37	$248.35	$248.40
7 purchase totals =	$983.20		$1,087.2269	$1,087.24	$1,087.20	$1,087.40