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	$77.84	6.244%	$82.7003	$82.70	$82.70	$82.70
Purchase #2	$180.93	9.661%	$198.4096	$198.41	$198.40	$198.40
Purchase #3	$114.56	8.193%	$123.9459	$123.95	$123.95	$123.90
Purchase #4	$109.38	11.690%	$122.1665	$122.17	$122.15	$122.20
Purchase #5	$38.64	12.450%	$43.4507	$43.45	$43.45	$43.50
Purchase #6	$8.25	3.638%	$8.5501	$8.55	$8.55	$8.60
Purchase #7	$40.26	12.360%	$45.2361	$45.24	$45.25	$45.20
7 purchase totals =	$569.86		$624.4592	$624.47	$624.45	$624.50