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	$157.28	13.216%	$178.0661	$178.07	$178.05	$178.10
Purchase #2	$40.87	12.296%	$45.8954	$45.90	$45.90	$45.90
Purchase #3	$129.86	5.726%	$137.2958	$137.30	$137.30	$137.30
Purchase #4	$22.64	12.388%	$25.4446	$25.44	$25.45	$25.40
Purchase #5	$112.48	3.836%	$116.7947	$116.79	$116.80	$116.80
Purchase #6	$90.49	10.683%	$100.157	$100.16	$100.15	$100.20
Purchase #7	$249.52	7.340%	$267.8348	$267.83	$267.85	$267.80
7 purchase totals =	$803.14		$871.4884	$871.49	$871.50	$871.50