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	$139.79	10.389%	$154.3128	$154.31	$154.30	$154.30
Purchase #2	$172.58	10.732%	$191.1013	$191.10	$191.10	$191.10
Purchase #3	$82.88	4.367%	$86.4994	$86.50	$86.50	$86.50
Purchase #4	$143.83	11.810%	$160.8163	$160.82	$160.80	$160.80
Purchase #5	$79.30	3.655%	$82.1984	$82.20	$82.20	$82.20
Purchase #6	$177.35	5.599%	$187.2798	$187.28	$187.30	$187.30
Purchase #7	$205.92	4.230%	$214.6304	$214.63	$214.65	$214.60
7 purchase totals =	$1,001.65		$1,076.8384	$1,076.84	$1,076.85	$1,076.80